Why does green mean go?
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The world is full of color, but how do our eyes see it? In this episode we’ll explain how color vision works, complete with a journey to a jazz club in the back of your eye. We’ll also look at the cultural meanings of the color red, we’ll find out about a new type of blue, and we’ll find out why stoplights use green to mean go. Our Moment of Um tackles the question, “why are bees black and yellow?”
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CYAN: You're listening to Brains On!, where we're serious about being curious.
SUBJECT 1: Brains On! is supported in part by a grant from the National Science Foundation
MOLLY BLOOM: Cyan, welcome to Brains On! headquarters. The studio is right this way.
CYAN: I'm so excited to be here.
MOLLY BLOOM: OK, so--
MARC SANCHEZ: Make sure you follow the traffic signal for direction.
MOLLY BLOOM: Traffic signal?
MARC SANCHEZ: Yeah, I installed this new hallway traffic signal to make sure things keep flowing smoothly here at Brains On! headquarters.
CYAN: Whoa, that is not the usual green-yellow-red traffic signal.
MARC SANCHEZ: Good eyes, Cyan. I made a few small tweaks, nothing too complicated.
MOLLY BLOOM: Small tweaks? Marc, there are now-- 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11-- 12 different color lights?
MARC SANCHEZ: Well, yeah. Green means go, red means stop, obviously. And yellow, as we know, means slow down. And blue means--
[SIGH]
Sit on the floor and think for a second. Orange means-- do cartwheels! Purple means dance in a funky manner. Turquoise means wave to the adoring imaginary crowd. Oh yeah, and this magenta one means--
[HUMMING]
Start humming. Chartreuse means you should pretend to be either riding a unicorn, or you are a unicorn yourself. I haven't quite decided which is better. And this pink one here--
[BUZZER SOUNDS]
Oh no, what does this pink one mean? I can't possibly have too many different colored lights, can I?
MOLLY BLOOM: No, wait. I like it.
CYAN: I bet pink means give Marc a high-five.
MARC SANCHEZ: Sure! Hold on. Pink light!
CYAN: High-five, Marc.
MOLLY BLOOM: My man.
MARC SANCHEZ: Now, purple light. Go ahead and dance yourselves to the studio.
MOLLY BLOOM: In a funky manner.
[FUNKY MUSIC PLAYS]
CYAN: See you, Marc.
MOLLY BLOOM: You're listening to Brains On! from American Public Media. I'm Molly Bloom, and I'm here with Cyan from Victoria, British Columbia. Hi, Cyan.
CYAN: Hi, Molly.
MOLLY BLOOM: This episode is a celebration of color. And Cyan, your name itself is a color. Can you describe what cyan looks like?
CYAN: Sure. Cyan is similar to the color of the sky when it's sunny out. It's a really nice blue.
MOLLY BLOOM: Oh, I love that description. So, how did your parents pick that name for you?
CYAN: My dad is an artist, and my mom also really likes art. So, they picked my name because they wanted something original and kind of related to colors.
MOLLY BLOOM: Have you ever met another Cyan before?
CYAN: I have never met another Cyan before.
MOLLY BLOOM: So, do you like being named after a color?
CYAN: Yeah, it's pretty cool to have a unique name.
MOLLY BLOOM: Do you do a lot of explaining about what your name means?
CYAN: Yeah. It's funny, because some people don't understand that I'm named after color, and it's funny because a lot of people don't understand how to say my name, too.
MOLLY BLOOM: What are some of the ways they say it?
CYAN: Sometimes, people will be like, oh, hi, "see-an" or "ky-an" or "sy-an." It's kind of funny.
MOLLY BLOOM: Yeah, we should probably say how it's spelled. It's spelled C-Y-A-N.
CYAN: Yes.
MOLLY BLOOM: So, do you have a favorite place where you see cyan in your life?
CYAN: Well, sometimes just laying in the grass, and just looking at the sky because, it's really similar to the color, cyan.
MOLLY BLOOM: That sounds lovely. Do you have other favorite colors, besides cyan?
CYAN: I really like the color lavender. It's like a light purple. It's just really calming and nice.
MOLLY BLOOM: So, this episode was inspired by one particular question from a listener that we found super fascinating.
MAXIMILIAN: My name is Maximilian. I come from Germany, and my question is, why is green the go color.
MOLLY BLOOM: That is a great question.
CYAN: Yeah, why isn't it purple or orange?
MOLLY BLOOM: As we were researching and working on answering this question, we found fascinating stories about other colors, too. We don't have time to delve into every color in this one episode, so we're focusing on three.
CYAN: Red, blue, and of course, green.
MOLLY BLOOM: Why these three? You might have heard about primary colors, the colors you can mix together to get other colors.
CYAN: Those are red, yellow, and blue when you're thinking of paint.
MOLLY BLOOM: But red, green, and blue are a different kind of primary color. If you have light from these three shades-- red, green, and blue-- you can mix them together to get all the colors of light.
CYAN: In fact, TVs, and phones, and computers, all use red, green, and blue to make all the images you see on a screen.
MOLLY BLOOM: Right. So we're going to dig into these three very important colors.
CYAN: But first, we have to make a pit stop to answer this question.
FINN: Hi, Brains On! My name is Finn and my question is, how does everything get its color?
MOLLY BLOOM: Well, let us illuminate you. Color starts with light.
CYAN: The main source of light in our galaxy is, our friend and yours, the sun.
MOLLY BLOOM: Our pal, the sun, beams out light we can see.
CYAN: That's called visible light. It's what colors our world.
MOLLY BLOOM: And this visible light has a range of energy levels in it. We see these different energy levels as different colors.
CYAN: So, when light hits something, some of these specific energies of light are reflected. Those are the colors we see.
MOLLY BLOOM: Other energies of light get absorbed by the object. So, we don't see those colors. So, when you see a bright orange salamander, for example, it means that light in that orange color range is bouncing off of your amphibian pal, and reaching your eyes, making you see it as orange.
CYAN: The salamander's skin absorbs the other colors of light, so you don't see those colors.
MOLLY BLOOM: If you stop to think about it, this is a mind-blowing fact. Sunlight and the white light from light bulbs actually contain all the colors at once.
[EXPLOSION]
CYAN: All the colors are shining down, all the time, but you only see certain ones when they get bounced back to the cells in your eyes.
MOLLY BLOOM: More on those cells in a second. But first, Cyan, are you ready to bounce around some ideas about the--
[MYSTERIOUS MUSIC PLAYS]
SUBJECT 2: (WHISPERING) Mystery sound.
CYAN: Yes.
MOLLY BLOOM: Here it is.
[MYSTERY SOUND PLAYS]
OK, Cyan, what is your guess?
CYAN: There's a beeping, and it also sounded like it was raining.
MOLLY BLOOM: Interesting. So, any thoughts about what could possibly be beeping, and some kind of rain sound?
CYAN: I don't know.
MOLLY BLOOM: OK, well, we're going to give you another chance to hear it, and guess again, a little bit later in the show.
GROUP: Brains on!
MOLLY BLOOM: Another big piece of how color works is our eyeball machinery. Brains On! producer Menaka Wilhelm is here to tell us more about that.
MENAKA WILHELM: Hi, Molly. Hi, Cyan. I talked to a physicist named Pupa Gilbert about this. And, Cyan, she's actually one of your fans.
PUPA GILBERT: My very favorite color is cyan, or turquoise, as I call it.
MENAKA WILHELM: And besides telling me how much she likes the color behind your name, she helped sketch out how we see all the colors, which-- prepare yourselves-- is going to take us to the very back of the eyeball, or the retina. Molly, do you have the zoom ray ready?
MOLLY BLOOM: Ready.
[RAY ZOOMS]
MENAKA WILHELM: Awesome.
CYAN: To the retina!
[RAY ZOOMS]
MOLLY BLOOM: Wow, there's a whole tiny world back here.
CYAN: There's even a jazz club.
MENAKA WILHELM: Yeah, we're headed there soon, actually. But first, the lay of the land. When light bounces off things in the world and into your eyeballs, cells back here notice that light and send messages to your brain.
PUPA GILBERT: So, these are specific types of brain cells that are sensitive to light.
MENAKA WILHELM: We have a couple of different kinds of these cells. There are rod cells and cone cells. Rod cells help us see in low-light situations. They're basically black and white vision. Cone cells, on the other hand, they sense colors. These are the ones we're talking about today. And get this, there are just three different kinds of cone cells that help us see the whole entire rainbow.
PUPA GILBERT: So, we see color through three different types of cones that are, for simplicity, called the red, green, and blue cones, in the back of our eye.
MENAKA WILHELM: Our eyes have millions of these cone cells, and each one is either a red cone, a blue cone, or a green cone.
MOLLY BLOOM: So, with just those three types of cones, the red, the green, and the blue, we can see all the colors?
MENAKA WILHELM: Exactly. They actually help you see other colors too, like yellow, and purple, and orange.
CYAN: How does that work?
MENAKA WILHELM: Well, to explain it, let's step into that jazz club you mentioned. You can think of the three cones as a little like a jazz trio.
[JAZZ MUSIC PLAYS]
[PLAYING PIANO NOTES]
LONG RED: Long Red, here on the keys. Reds get my jets going.
[PLAYING SAXOPHONE]
MEZZO GREENO: And Mezzo Greeno is my name. The saxophone is my game. That's Mezzo like middle, since I'm into greens, the in-betweens of the rainbow.
[PLAYING BASS GUITAR]
BLUES SHORTY: Plucking this base, Blues Shorty here. Blues hit me right in my feels.
CYAN: So, those are cone cells?
MENAKA WILHELM: Yep. We sometimes call these the red, green, and blue cones, but each cone really senses a whole range of colors.
PUPA GILBERT: It's not as if the red cones are only sensitive to red light. They're actually sensitive to a very broad range.
MENAKA WILHELM: That's important, because there are a lot of colors to see.
BLUES SHORTY: Sure are. This rainbow trio wants you to see them all.
LONG RED: So, when the light hits us, we play the brain a tune, describing what we see.
MEZZO GREENO: Your brain makes our beautiful signals into your mental picture of the world.
[PLAYING NOTES]
MENAKA WILHELM: Since each cone signals for a range of colors, you can think of Long Red, that red cone, playing reds, and also oranges and yellows, and even some greens. So, most colors set off more than one cone at once.
BLUES SHORTY: Right, we're just not that big on solos.
MENAKA WILHELM: And when two cones respond to the same color, their signals will be at different levels. For this trio, you can think about different cones playing together, but at a different volume.
BLUES SHORTY: When you're looking at a deep purple plum, I play nice and loud. Because remember, I don't just play blues, also purples too.
LONG RED: And I join in, hit a couple of notes quietly, even though that might surprise you. I may be Long Red, but I sense some purple light as well.
MEZZO GREENO: So do I, even though my forte is green. But I just pick up a little purple, so it's just like a quiet little ditty.
MENAKA WILHELM: So that purple plum is really a mix of signals from each cone. Same with orange, even though none of these cones ever get called orange cones.
BLUES SHORTY: Orange cones belong on the road, directing traffic, not in the eye. We handle orange just fine on our own.
LONG RED: Like, say you're looking at an orange cat. I play the loudest. Mezzo Greeno backs me up, and Blues Shorty keeps his volume real low.
MENAKA WILHELM: These different signals from all three cones are almost a little code. The brain can decode it, and each translation becomes a color you see. And these multitalented cones sound just great.
[JAZZ MUSIC PLAYING]
[CHEERS, APPLAUSE]
It seems like this jazz trio is taking a break. Molly, can you zoom us out to our normal sizes?
MOLLY BLOOM: Absolutely.
[RAY ZOOMS]
MENAKA WILHELM: All right, nice shrinky-dinking with you all, but I've got to scoot. See you soon.
CYAN: Thanks, Menaka.
MENAKA WILHELM: Any time. Bye!
[BICYCLE BELL RINGS]
SUBJECT 3: Brains, brains, brains on.
MOLLY BLOOM: Now that we've explored how we see colors, let's get to know those three main ones a little better. Red, blue, and green.
CYAN: And red is up first.
MOLLY BLOOM: We thought red would be a good place to start, because it's a powerful color that can stir up a lot of feelings.
CYAN: Which is something Brains On! listeners have wondered about.
ENYA: My name is Enya, and I live in Houston, Texas. My question is, why are certain colors associated with certain moods or emotions?
VIOLA: Hi, my name is Viola. I'm nine years old, and my question is, why do people like certain colors?
ZOE: My name is Zoe, from Manheim, Pennsylvania. And I want to know, do different colors affect how we feel?
KASSIA ST CLAIR: So, this is a really interesting one. There are essentially a few different reasons why colors can really affect people.
CYAN: That's Kassia St Clair.
MOLLY BLOOM: She's a writer and color expert who wrote the book, The Secret Lives of Colour.
KASSIA ST CLAIR: Some of it is cultural. For example, in the West, if you think of royalty, and you are asked to associate a color with royalty, most people will often say purple. And that is, in part, because in the ancient world, there was a very expensive purple dye, that was actually made from sea snails, that was purple, and was reserved almost exclusively for royalty.
MOLLY BLOOM: Oh, your royal cape is so divine.
CYAN: Why, thank you. It's made from the finest sea snails.
KASSIA ST CLAIR: But, if you were to ask someone in China what color they associated with royalty, they would most likely say yellow. Because in China, a yellow dye was reserved for royalty.
MOLLY BLOOM: Kassia told us that colors can have personal associations too.
CYAN: For example, if your bedroom is painted green, and you do fun stuff in there-- read stories, play with toys, listen to podcasts-- you might associate the color green with feeling happy.
MOLLY BLOOM: And green might bring on the same feelings as you get older, even if you have a new room in a different color.
CYAN: But we're here to talk about red.
MOLLY BLOOM: Right. Cyan, when you think of red, what comes to mind?
CYAN: I think of red fruit and vegetables, like apples and strawberries. And then, I think of dragons.
MOLLY BLOOM: I like that. Well, Kassia says that throughout history, people have been very interested in red.
KASSIA ST CLAIR: Red has always had this really important place in human culture. It's very often associated with burials, you very often find red pigments or red dyed cloth in graves, all over the world, from China to South America to Europe. In ancient Egypt, there's a god of the afterlife, who's also known by the name Lord of the Red Cloth. And, very often, in Egyptian burials, mummies were often found with cloth that had been dyed red with a pigment or colorant called hematite.
CYAN: Hematite is a pigment that comes from iron in the Earth. It can be used as a dye or paint.
MOLLY BLOOM: So you've probably seen that red-orange color that metal gets when it's rusty. If you took that metal and wiped it on your shirt, then you'd basically be doing the same thing as the ancient Egyptians.
CYAN: Kassia says that people found other natural ways to make red too.
KASSIA ST CLAIR: You also get red dyes that are produced by insects, believe it or not. Tiny, tiny insects that are so small, they almost look like grains of rice. But when you squish them, they produce a very powerful red colorant, and this is called cochineal. The best types of cochineal come from South and Central America, and are, in fact, still use today as a food coloring and as a coloring in cosmetics.
MOLLY BLOOM: Nobody can really say why people have been drawn to red for so long, but its popularity is clear, even to this day.
KASSIA ST CLAIR: It seems to be near universal that red has a power over us, that can be seen throughout all cultures, and over a vast range of time. And so, it's very difficult to tell, because we do have all these personal feelings, and it's very difficult to untangle what colors mean to us.
But there's no denying that color has the power to influence our mood, and to make us feel happy or sad, or to remember certain people or friends. And in that way, color has a real power over us, and is incredibly important in our lives, even if we don't always know exactly why.
[UPBEAT MUSIC PLAYING]
MOLLY BLOOM: Clearly, colors can inspire a lot of feelings, but they can inspire other things, too.
CYAN: Like superheroes.
MOLLY BLOOM: Oh, yeah. We asked you to dream up a color hero for this episode, and you sent us some super creative ideas.
[UPLIFTING MUSIC PLAYING]
ELLIE: Hi, my name is Ellie, and I am from Folsom, California. My color superhero is Super Silver. She can give silver to people in need.
MAX: Hello, my name is Max from Basel, Switzerland. My color superhero would be Aqua Ninja. He can control water and stand on water.
MATTHEW: Hi, Brains On! My name is Matthew, and I am from New Westminster, BC. My superhero's name is Mr. Planto, and he is the color green. He can fight pollution, and grow any plants in the world. And his sidekick's name is Planty. He can destroy pollution, or anything he wants, and he can make a plant wall. Thank you.
TUPELO: My name is Tupelo. I am from Minneapolis, Minnesota. My superhero's name is Rainbow Star. Her powers are, she can shoot rainbows from her hands, and she spreads lots of color all around the world.
MOLLY BLOOM: We've got more color heroes coming up.
CYAN: Plus, we're diving into deep blue and gorgeous green, right after this.
[MUSIC PLAYING]
MOLLY BLOOM: Do you have a mystery sound you want to share with us?
CYAN: A question you want answered on the show?
MOLLY BLOOM: Or maybe a drawing of your fabulous color superhero?
CYAN: Send those all to us at BrainsOn.org/contact.
MOLLY BLOOM: That's what this listener did.
GABE: My name is Gabe, from Brighton, Michigan. My question is, why are bees black and yellow?
CYAN: We'll be back with the answer to that question at the end of the show.
MOLLY BLOOM: That's our Moment of Um.
CYAN: And we'll have the most recent group of listeners to be added to the Brains Honor Roll.
MOLLY BLOOM: We also want to hear from you for an episode we're working on right now, about tiny robots. We want to know, if you could invent a tiny robot, what would it do and what noise would it make. My tiny robot would vacuum up pollen before it could get to my nose, and it would sound like this--
[IMITATES ROBOT WHOOSHING]
Share your tiny robot jobs and noises with us, at BrainsOn.org/contact. Can't wait to hear from you.
[UPLIFTING MUSIC PLAYING]
ANDREW: Hi, Brains On! My name is Andrew, and I live in New Westminster, BC, Canada. My colored superhero is red, and he's called Oxygenist. His superpower is he breathes in carbon dioxide and breathes out oxygen. I gave him this superpower because he will solve climate change and global warming.
SUMMER: Hi, I'm Summer, and my color superhero's color is blue. Its name is Sea Blue, and its superpowers are to control the sea.
JACK: Hi, Brains On! My name is Jack, from San Antonio, Texas. And my color superhero is Red Fire. He shoots fire out of his eyes.
AMIR: Hi, my name is Amir, and I am a 10-year-old from Zionsville, Indiana. My color-inspired superhero is named Purple Petite. Her superpower is that she can squeeze through tiny spaces. She lives in Color Kingdom, and her enemies are the Jasper Junk Food Bandits. They try to convince Color Kingdom into only eating junk food. Dun dun dun!
MOLLY BLOOM: You are listening to Brains On! from American Public Media. I'm Molly.
CYAN: And I'm Cyan.
RUBY GUTHRIE: And I'm Ruby.
MOLLY BLOOM: Hey, it's our friend Ruby Guthrie. She's here with a story about blue.
RUBY GUTHRIE: Hi, Molly. Hi, Cyan. So far, we've talked a lot about how we see colors, and what different colors mean. But have you ever wondered how you make a color?
CYAN: I have a rough idea. Usually, I think of paint, and just mixing the primary colors together. Yeah, you can create a lot of colors that way. Listeners Jonah and Kayla also had some colorful questions.
KAYLA: Hi, my name is Kayla, and I live in Davis, California.
JONAH: Hi, I'm Jonah from Ventura, California.
KAYLA: My question is, how do people make color?
JONAH: My question is, how are colors created?
RUBY GUTHRIE: Great questions. And I was curious too, so I talked to Mas Subramanian. He's a chemistry professor at Oregon State University. About 10 years ago, Mas created a color in his lab, but it happened all by accident.
[MUSIC PLAYING]
One day, Mas was in his lab, and he was mixing different chemicals, trying to create a new material for computers. He told his grad student to mix three compounds containing three elements-- yttrium, that's white, indium, which is yellow, and manganese, that's black. They took these materials and heated them up in a super hot oven. This way, all the elements could mix together to form a new compound-- kind of like when you bake a cake.
[OVEN DINGS]
But when they took it out, they were shocked.
MAS SUBRAMANIAN: I noticed that they came out stunningly blue, which I did not expect. Now, imagine my surprise, because I started with materials that were white, yellow, and black in color, and out came this brilliant blue.
RUBY GUTHRIE: Mas named it YInMn blue after the three elements, yttrium, indium, and manganese. Now, YInMn blue isn't a new color, per se, but rather a new blue pigment. A pigment is usually a powder that you use to add color to other things, like paint ink, or cloth. And civilizations have struggled for centuries trying to make blue pigments, mostly because it's such a rare color. There aren't many things that are naturally blue. And if you try to create blue with chemistry, it can be tricky to get it right.
For example, in the Renaissance period, painters used ultramarine, a pigment made from the gemstone, lapis lazuli. Ultramarine was ultra-expensive, because not only was it made from a rare material, but it also took weeks to extract the color. Since this took so much work, sometimes, ultramarine cost more than gold. So, when Mas realized he had made such a vivid blue, he put his computer work on hold to look more into his new discovery.
MAS SUBRAMANIAN: Immediately, I recognized these compounds may have a potential to be useful as blue pigment, as they are very stable. No change in color when exposed to very high temperatures.
RUBY GUTHRIE: Mas just said that this blue is really stable. That means it doesn't change much when it comes in contact with things like heat, water, or even acid. That makes it super tough and long-lasting, which is great for painting things like cars and buildings. It's so cool, literally. Not only is blue a cool-toned color, but YInMn mean blue actually deflects heat, meaning heat bounces off of it. So, it stays cool, even if it's exposed to really hot temperatures.
MAS SUBRAMANIAN: So, if you coat a building or a car with YInMn in blue, it can keep the building cooler, or the car cooler, during summertime. So, otherwise we call this as a cool pigment. So, that makes it very special, because no other blue pigment actually deflects heat.
RUBY GUTHRIE: Now, that's chilling in a freezer with sunglasses kind of cool. And to think it all started with an accident.
MAS SUBRAMANIAN: Most of the amazing discoveries come by accident. Not everything can be predicted, or never everything can be discovered by planning. I tell my students, don't think too much, just do it in the lab, and you may be able to create something interesting, actually.
RUBY GUTHRIE: Mas is totally right. A lot of times, I think, we think of accidents as bad things. But, they can actually be a really good chance for us to learn and explore. And his accident is leading to even more exploring. Mas is now trying to make a red pigment that's as stable as YInMn blue. So, keep experimenting. You never know what you might discover.
MOLLY BLOOM: Thanks, Ruby.
RUBY GUTHRIE: Thank you. And I'm off to the kitchen, I'm really craving some blueberries.
MOLLY BLOOM: All right, Cyan. Are you ready to hear the mystery sound one more time?
CYAN: Yes.
MOLLY BLOOM: OK, here it is.
[MYSTERY SOUND PLAYS]
OK, any new thoughts?
CYAN: Maybe a car backing up in the rain?
MOLLY BLOOM: Oh, good thought. Sometimes when cars back up, they make that beeping sound. Excellent thought. Well, we're going to hear it again, and this time there's a hint in the sound.
CYAN: OK.
[MYSTERY SOUND PLAYS]
SUBJECT 4: California.
[INDISTINCT]
California. California,
[INDISTINCT]
MOLLY BLOOM: OK, what do you think, now that you heard that more complete sound?
CYAN: Maybe a plane landing?
MOLLY BLOOM: Oh, yeah, because I heard the word "California" in there.
CYAN: Yeah.
MOLLY BLOOM: That's an excellent guess. Well, that is the sound of a signal at a crosswalk.
CYAN: Oh.
MOLLY BLOOM: So, you know sometimes they have those voices that talk to you while you're waiting for the crosswalk?
CYAN: Yeah.
MOLLY BLOOM: At some traffic intersections, the signals beep one way to tell you to wait, and change to a different beep when it's time to go. And that brings us back to that very important color question.
MAXIMILIAN: Why is green the go color?
MOLLY BLOOM: We asked our resident plant lover, and general green thing enthusiast, Sanden Totten, to look into this.
SANDEN TOTTEN: Oh, I love talking about green. Did you know George Washington loved the color? He called it "grateful to the eye." And studies suggest, just looking at green boosts your creativity. And right, one of green's most important roles is being the go color.
[ENGINE ROARS]
But why? I asked historian Megan Kate Nelson to weigh in.
MEGAN KATE NELSON: The green for go and the red for stop came from the railroad industry.
SANDEN TOTTEN: It turns out, stoplight inventors picked green since it worked so well for trains. But get this, originally, for trains, white was the go color. What? I know! Check it out.
[COUNTRY MUSIC PLAYS]
This was before lights ran on electricity. Back then, you didn't flick a switch or press a button to turn on a light. Oh, no. You lit a match to light a lamp. Lamps were basically teeny-tiny fires in a container. Picture a metal cylinder with a light from a fire shining through a glass window. That's a lamp. Megan Kate Nelson, our historian friend, says back then, train stations lit a plain white lamp to mean go. To mean stop, they simply covered the same lantern with a red glass cover.
MEGAN KATE NELSON: They ran into some problems when they were using white as go, because sometimes, the red glass would break, and then it would be all white.
SANDEN TOTTEN: Oof, yeah. Mixing up stop and go, that's very bad news.
MEGAN KATE NELSON: They changed it to green, so that you had a very clear difference.
SANDEN TOTTEN: That way, if the green glass broke-- which happened from time to time-- conductors would know something was up, because the light was white, not green or red. But wait, so, why did railroads pick green for go? I mean, why not purple or blue? Well, it seems like railroads chose it because factories used it.
MEGAN KATE NELSON: The very first factories that created all kinds of different objects had really big machines, and you could tell that they were on or off from the noise. But you also flipped a switch to turn them on, and that switch was often green.
SANDEN TOTTEN: Now, it's hard to find an explanation for why green was used in early factories. My friends, it's a secret loss to the green mists of time. But maybe, it was because green things rule. These factory people could have been inspired by green ferns, or green emeralds. Probably not green boogers, but maybe green parakeets? Or green algae? Or grasshoppers. Ooh, praying mantises, four-leaf clovers, three-leaf clovers, five-leaf clovers, green mold on bread. Probably not green mold. Maybe Ninja Turtles, gremlin, green mint leaves.
MOLLY BLOOM: Colors happen because of bouncing light.
CYAN: The light that bounces off of something is the color you see.
MOLLY BLOOM: Eyes take in colors with special cells called cone cells.
CYAN: Then, the brain builds a picture of what the world looks like.
MOLLY BLOOM: Red has been used as a powerful symbol in many cultures throughout history.
CYAN: People associate different colors with different feelings, depending on where they might have first experienced that color.
MOLLY BLOOM: Blue was once a really rare color pigment, but scientists are finding new ways to create it.
CYAN: Green first started to mean go in factories, then railroads, and eventually, stoplights.
MOLLY BLOOM: That's it for this episode of Brains On!
CYAN: It was produced by Menaka Wilhelm, Marc Sanchez, Sanden Totten, and Molly Bloom.
MOLLY BLOOM: We had production help from Sabby Robinson, Ruby Guthrie, and Christina Lopez, and engineering help from John Miller. Special thanks to Ladena Racine, Olivia Kuzio, Luke Burbank, Andrew Walsh, Rosie DuPont, and Libby Dinkman.
CYAN: Now, before we go, it's time for our Moment of Um--
SEVERAL VOICES: Um--
GABE: My question is, why are bees black and yellow?
DAN CARIVEAU: There's a fancy term for that. It's called aposematic coloration. And what that does is it tells predators not to eat it.
My name is Dan Cariveau. In Minnesota, I'm an assistant professor of entomology. Entomology, by the way, is the study of insects. And I look at native bees. So when we think of bees, we can think of things like a honey bee.
But in reality, there's 20,000 or more species of bees on Earth. And so we study those other bees. If you think about it, the black and the yellow, they're very high contrast in colors.
So you have this very dark black and then a very bright yellow. And what that does is it makes it very easy to see as opposed to something that might be green and drab. And so it's very easy. And what that does is it helps tell predators that, in fact, this is something you don't want to eat. It's something you don't want to touch, that really bright coloration.
There's a number of other animals that do this. So things like coral snakes or poison arrow frogs. There are butterflies that are poisonous that all look alike. And that helps them realize that the predators shouldn't eat them.
As I mentioned, there's 20,000 species of bees on Earth. And actually, most of them are not yellow and black. So we have all different colors of bees. There's greens and there's blues, and there's all sorts of browns and blacks. So go ahead and look at all the different species that are out there. They're fascinating.
TICKLED PINK: I'm Tickled Pink to read this list of names. It's time for the Brains Honor Roll. These are the amazing listeners who shared their questions, ideas, mystery sounds, drawings, and high fives with us.
[LISTING HONOR ROLL]
Brains On will be back soon with more answers to your questions.
SUBJECT: Thanks for listening.
SUBJECT 1: Brains On! is supported in part by a grant from the National Science Foundation
MOLLY BLOOM: Cyan, welcome to Brains On! headquarters. The studio is right this way.
CYAN: I'm so excited to be here.
MOLLY BLOOM: OK, so--
MARC SANCHEZ: Make sure you follow the traffic signal for direction.
MOLLY BLOOM: Traffic signal?
MARC SANCHEZ: Yeah, I installed this new hallway traffic signal to make sure things keep flowing smoothly here at Brains On! headquarters.
CYAN: Whoa, that is not the usual green-yellow-red traffic signal.
MARC SANCHEZ: Good eyes, Cyan. I made a few small tweaks, nothing too complicated.
MOLLY BLOOM: Small tweaks? Marc, there are now-- 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11-- 12 different color lights?
MARC SANCHEZ: Well, yeah. Green means go, red means stop, obviously. And yellow, as we know, means slow down. And blue means--
[SIGH]
Sit on the floor and think for a second. Orange means-- do cartwheels! Purple means dance in a funky manner. Turquoise means wave to the adoring imaginary crowd. Oh yeah, and this magenta one means--
[HUMMING]
Start humming. Chartreuse means you should pretend to be either riding a unicorn, or you are a unicorn yourself. I haven't quite decided which is better. And this pink one here--
[BUZZER SOUNDS]
Oh no, what does this pink one mean? I can't possibly have too many different colored lights, can I?
MOLLY BLOOM: No, wait. I like it.
CYAN: I bet pink means give Marc a high-five.
MARC SANCHEZ: Sure! Hold on. Pink light!
CYAN: High-five, Marc.
MOLLY BLOOM: My man.
MARC SANCHEZ: Now, purple light. Go ahead and dance yourselves to the studio.
MOLLY BLOOM: In a funky manner.
[FUNKY MUSIC PLAYS]
CYAN: See you, Marc.
MOLLY BLOOM: You're listening to Brains On! from American Public Media. I'm Molly Bloom, and I'm here with Cyan from Victoria, British Columbia. Hi, Cyan.
CYAN: Hi, Molly.
MOLLY BLOOM: This episode is a celebration of color. And Cyan, your name itself is a color. Can you describe what cyan looks like?
CYAN: Sure. Cyan is similar to the color of the sky when it's sunny out. It's a really nice blue.
MOLLY BLOOM: Oh, I love that description. So, how did your parents pick that name for you?
CYAN: My dad is an artist, and my mom also really likes art. So, they picked my name because they wanted something original and kind of related to colors.
MOLLY BLOOM: Have you ever met another Cyan before?
CYAN: I have never met another Cyan before.
MOLLY BLOOM: So, do you like being named after a color?
CYAN: Yeah, it's pretty cool to have a unique name.
MOLLY BLOOM: Do you do a lot of explaining about what your name means?
CYAN: Yeah. It's funny, because some people don't understand that I'm named after color, and it's funny because a lot of people don't understand how to say my name, too.
MOLLY BLOOM: What are some of the ways they say it?
CYAN: Sometimes, people will be like, oh, hi, "see-an" or "ky-an" or "sy-an." It's kind of funny.
MOLLY BLOOM: Yeah, we should probably say how it's spelled. It's spelled C-Y-A-N.
CYAN: Yes.
MOLLY BLOOM: So, do you have a favorite place where you see cyan in your life?
CYAN: Well, sometimes just laying in the grass, and just looking at the sky because, it's really similar to the color, cyan.
MOLLY BLOOM: That sounds lovely. Do you have other favorite colors, besides cyan?
CYAN: I really like the color lavender. It's like a light purple. It's just really calming and nice.
MOLLY BLOOM: So, this episode was inspired by one particular question from a listener that we found super fascinating.
MAXIMILIAN: My name is Maximilian. I come from Germany, and my question is, why is green the go color.
MOLLY BLOOM: That is a great question.
CYAN: Yeah, why isn't it purple or orange?
MOLLY BLOOM: As we were researching and working on answering this question, we found fascinating stories about other colors, too. We don't have time to delve into every color in this one episode, so we're focusing on three.
CYAN: Red, blue, and of course, green.
MOLLY BLOOM: Why these three? You might have heard about primary colors, the colors you can mix together to get other colors.
CYAN: Those are red, yellow, and blue when you're thinking of paint.
MOLLY BLOOM: But red, green, and blue are a different kind of primary color. If you have light from these three shades-- red, green, and blue-- you can mix them together to get all the colors of light.
CYAN: In fact, TVs, and phones, and computers, all use red, green, and blue to make all the images you see on a screen.
MOLLY BLOOM: Right. So we're going to dig into these three very important colors.
CYAN: But first, we have to make a pit stop to answer this question.
FINN: Hi, Brains On! My name is Finn and my question is, how does everything get its color?
MOLLY BLOOM: Well, let us illuminate you. Color starts with light.
CYAN: The main source of light in our galaxy is, our friend and yours, the sun.
MOLLY BLOOM: Our pal, the sun, beams out light we can see.
CYAN: That's called visible light. It's what colors our world.
MOLLY BLOOM: And this visible light has a range of energy levels in it. We see these different energy levels as different colors.
CYAN: So, when light hits something, some of these specific energies of light are reflected. Those are the colors we see.
MOLLY BLOOM: Other energies of light get absorbed by the object. So, we don't see those colors. So, when you see a bright orange salamander, for example, it means that light in that orange color range is bouncing off of your amphibian pal, and reaching your eyes, making you see it as orange.
CYAN: The salamander's skin absorbs the other colors of light, so you don't see those colors.
MOLLY BLOOM: If you stop to think about it, this is a mind-blowing fact. Sunlight and the white light from light bulbs actually contain all the colors at once.
[EXPLOSION]
CYAN: All the colors are shining down, all the time, but you only see certain ones when they get bounced back to the cells in your eyes.
MOLLY BLOOM: More on those cells in a second. But first, Cyan, are you ready to bounce around some ideas about the--
[MYSTERIOUS MUSIC PLAYS]
SUBJECT 2: (WHISPERING) Mystery sound.
CYAN: Yes.
MOLLY BLOOM: Here it is.
[MYSTERY SOUND PLAYS]
OK, Cyan, what is your guess?
CYAN: There's a beeping, and it also sounded like it was raining.
MOLLY BLOOM: Interesting. So, any thoughts about what could possibly be beeping, and some kind of rain sound?
CYAN: I don't know.
MOLLY BLOOM: OK, well, we're going to give you another chance to hear it, and guess again, a little bit later in the show.
GROUP: Brains on!
MOLLY BLOOM: Another big piece of how color works is our eyeball machinery. Brains On! producer Menaka Wilhelm is here to tell us more about that.
MENAKA WILHELM: Hi, Molly. Hi, Cyan. I talked to a physicist named Pupa Gilbert about this. And, Cyan, she's actually one of your fans.
PUPA GILBERT: My very favorite color is cyan, or turquoise, as I call it.
MENAKA WILHELM: And besides telling me how much she likes the color behind your name, she helped sketch out how we see all the colors, which-- prepare yourselves-- is going to take us to the very back of the eyeball, or the retina. Molly, do you have the zoom ray ready?
MOLLY BLOOM: Ready.
[RAY ZOOMS]
MENAKA WILHELM: Awesome.
CYAN: To the retina!
[RAY ZOOMS]
MOLLY BLOOM: Wow, there's a whole tiny world back here.
CYAN: There's even a jazz club.
MENAKA WILHELM: Yeah, we're headed there soon, actually. But first, the lay of the land. When light bounces off things in the world and into your eyeballs, cells back here notice that light and send messages to your brain.
PUPA GILBERT: So, these are specific types of brain cells that are sensitive to light.
MENAKA WILHELM: We have a couple of different kinds of these cells. There are rod cells and cone cells. Rod cells help us see in low-light situations. They're basically black and white vision. Cone cells, on the other hand, they sense colors. These are the ones we're talking about today. And get this, there are just three different kinds of cone cells that help us see the whole entire rainbow.
PUPA GILBERT: So, we see color through three different types of cones that are, for simplicity, called the red, green, and blue cones, in the back of our eye.
MENAKA WILHELM: Our eyes have millions of these cone cells, and each one is either a red cone, a blue cone, or a green cone.
MOLLY BLOOM: So, with just those three types of cones, the red, the green, and the blue, we can see all the colors?
MENAKA WILHELM: Exactly. They actually help you see other colors too, like yellow, and purple, and orange.
CYAN: How does that work?
MENAKA WILHELM: Well, to explain it, let's step into that jazz club you mentioned. You can think of the three cones as a little like a jazz trio.
[JAZZ MUSIC PLAYS]
[PLAYING PIANO NOTES]
LONG RED: Long Red, here on the keys. Reds get my jets going.
[PLAYING SAXOPHONE]
MEZZO GREENO: And Mezzo Greeno is my name. The saxophone is my game. That's Mezzo like middle, since I'm into greens, the in-betweens of the rainbow.
[PLAYING BASS GUITAR]
BLUES SHORTY: Plucking this base, Blues Shorty here. Blues hit me right in my feels.
CYAN: So, those are cone cells?
MENAKA WILHELM: Yep. We sometimes call these the red, green, and blue cones, but each cone really senses a whole range of colors.
PUPA GILBERT: It's not as if the red cones are only sensitive to red light. They're actually sensitive to a very broad range.
MENAKA WILHELM: That's important, because there are a lot of colors to see.
BLUES SHORTY: Sure are. This rainbow trio wants you to see them all.
LONG RED: So, when the light hits us, we play the brain a tune, describing what we see.
MEZZO GREENO: Your brain makes our beautiful signals into your mental picture of the world.
[PLAYING NOTES]
MENAKA WILHELM: Since each cone signals for a range of colors, you can think of Long Red, that red cone, playing reds, and also oranges and yellows, and even some greens. So, most colors set off more than one cone at once.
BLUES SHORTY: Right, we're just not that big on solos.
MENAKA WILHELM: And when two cones respond to the same color, their signals will be at different levels. For this trio, you can think about different cones playing together, but at a different volume.
BLUES SHORTY: When you're looking at a deep purple plum, I play nice and loud. Because remember, I don't just play blues, also purples too.
LONG RED: And I join in, hit a couple of notes quietly, even though that might surprise you. I may be Long Red, but I sense some purple light as well.
MEZZO GREENO: So do I, even though my forte is green. But I just pick up a little purple, so it's just like a quiet little ditty.
MENAKA WILHELM: So that purple plum is really a mix of signals from each cone. Same with orange, even though none of these cones ever get called orange cones.
BLUES SHORTY: Orange cones belong on the road, directing traffic, not in the eye. We handle orange just fine on our own.
LONG RED: Like, say you're looking at an orange cat. I play the loudest. Mezzo Greeno backs me up, and Blues Shorty keeps his volume real low.
MENAKA WILHELM: These different signals from all three cones are almost a little code. The brain can decode it, and each translation becomes a color you see. And these multitalented cones sound just great.
[JAZZ MUSIC PLAYING]
[CHEERS, APPLAUSE]
It seems like this jazz trio is taking a break. Molly, can you zoom us out to our normal sizes?
MOLLY BLOOM: Absolutely.
[RAY ZOOMS]
MENAKA WILHELM: All right, nice shrinky-dinking with you all, but I've got to scoot. See you soon.
CYAN: Thanks, Menaka.
MENAKA WILHELM: Any time. Bye!
[BICYCLE BELL RINGS]
SUBJECT 3: Brains, brains, brains on.
MOLLY BLOOM: Now that we've explored how we see colors, let's get to know those three main ones a little better. Red, blue, and green.
CYAN: And red is up first.
MOLLY BLOOM: We thought red would be a good place to start, because it's a powerful color that can stir up a lot of feelings.
CYAN: Which is something Brains On! listeners have wondered about.
ENYA: My name is Enya, and I live in Houston, Texas. My question is, why are certain colors associated with certain moods or emotions?
VIOLA: Hi, my name is Viola. I'm nine years old, and my question is, why do people like certain colors?
ZOE: My name is Zoe, from Manheim, Pennsylvania. And I want to know, do different colors affect how we feel?
KASSIA ST CLAIR: So, this is a really interesting one. There are essentially a few different reasons why colors can really affect people.
CYAN: That's Kassia St Clair.
MOLLY BLOOM: She's a writer and color expert who wrote the book, The Secret Lives of Colour.
KASSIA ST CLAIR: Some of it is cultural. For example, in the West, if you think of royalty, and you are asked to associate a color with royalty, most people will often say purple. And that is, in part, because in the ancient world, there was a very expensive purple dye, that was actually made from sea snails, that was purple, and was reserved almost exclusively for royalty.
MOLLY BLOOM: Oh, your royal cape is so divine.
CYAN: Why, thank you. It's made from the finest sea snails.
KASSIA ST CLAIR: But, if you were to ask someone in China what color they associated with royalty, they would most likely say yellow. Because in China, a yellow dye was reserved for royalty.
MOLLY BLOOM: Kassia told us that colors can have personal associations too.
CYAN: For example, if your bedroom is painted green, and you do fun stuff in there-- read stories, play with toys, listen to podcasts-- you might associate the color green with feeling happy.
MOLLY BLOOM: And green might bring on the same feelings as you get older, even if you have a new room in a different color.
CYAN: But we're here to talk about red.
MOLLY BLOOM: Right. Cyan, when you think of red, what comes to mind?
CYAN: I think of red fruit and vegetables, like apples and strawberries. And then, I think of dragons.
MOLLY BLOOM: I like that. Well, Kassia says that throughout history, people have been very interested in red.
KASSIA ST CLAIR: Red has always had this really important place in human culture. It's very often associated with burials, you very often find red pigments or red dyed cloth in graves, all over the world, from China to South America to Europe. In ancient Egypt, there's a god of the afterlife, who's also known by the name Lord of the Red Cloth. And, very often, in Egyptian burials, mummies were often found with cloth that had been dyed red with a pigment or colorant called hematite.
CYAN: Hematite is a pigment that comes from iron in the Earth. It can be used as a dye or paint.
MOLLY BLOOM: So you've probably seen that red-orange color that metal gets when it's rusty. If you took that metal and wiped it on your shirt, then you'd basically be doing the same thing as the ancient Egyptians.
CYAN: Kassia says that people found other natural ways to make red too.
KASSIA ST CLAIR: You also get red dyes that are produced by insects, believe it or not. Tiny, tiny insects that are so small, they almost look like grains of rice. But when you squish them, they produce a very powerful red colorant, and this is called cochineal. The best types of cochineal come from South and Central America, and are, in fact, still use today as a food coloring and as a coloring in cosmetics.
MOLLY BLOOM: Nobody can really say why people have been drawn to red for so long, but its popularity is clear, even to this day.
KASSIA ST CLAIR: It seems to be near universal that red has a power over us, that can be seen throughout all cultures, and over a vast range of time. And so, it's very difficult to tell, because we do have all these personal feelings, and it's very difficult to untangle what colors mean to us.
But there's no denying that color has the power to influence our mood, and to make us feel happy or sad, or to remember certain people or friends. And in that way, color has a real power over us, and is incredibly important in our lives, even if we don't always know exactly why.
[UPBEAT MUSIC PLAYING]
MOLLY BLOOM: Clearly, colors can inspire a lot of feelings, but they can inspire other things, too.
CYAN: Like superheroes.
MOLLY BLOOM: Oh, yeah. We asked you to dream up a color hero for this episode, and you sent us some super creative ideas.
[UPLIFTING MUSIC PLAYING]
ELLIE: Hi, my name is Ellie, and I am from Folsom, California. My color superhero is Super Silver. She can give silver to people in need.
MAX: Hello, my name is Max from Basel, Switzerland. My color superhero would be Aqua Ninja. He can control water and stand on water.
MATTHEW: Hi, Brains On! My name is Matthew, and I am from New Westminster, BC. My superhero's name is Mr. Planto, and he is the color green. He can fight pollution, and grow any plants in the world. And his sidekick's name is Planty. He can destroy pollution, or anything he wants, and he can make a plant wall. Thank you.
TUPELO: My name is Tupelo. I am from Minneapolis, Minnesota. My superhero's name is Rainbow Star. Her powers are, she can shoot rainbows from her hands, and she spreads lots of color all around the world.
MOLLY BLOOM: We've got more color heroes coming up.
CYAN: Plus, we're diving into deep blue and gorgeous green, right after this.
[MUSIC PLAYING]
MOLLY BLOOM: Do you have a mystery sound you want to share with us?
CYAN: A question you want answered on the show?
MOLLY BLOOM: Or maybe a drawing of your fabulous color superhero?
CYAN: Send those all to us at BrainsOn.org/contact.
MOLLY BLOOM: That's what this listener did.
GABE: My name is Gabe, from Brighton, Michigan. My question is, why are bees black and yellow?
CYAN: We'll be back with the answer to that question at the end of the show.
MOLLY BLOOM: That's our Moment of Um.
CYAN: And we'll have the most recent group of listeners to be added to the Brains Honor Roll.
MOLLY BLOOM: We also want to hear from you for an episode we're working on right now, about tiny robots. We want to know, if you could invent a tiny robot, what would it do and what noise would it make. My tiny robot would vacuum up pollen before it could get to my nose, and it would sound like this--
[IMITATES ROBOT WHOOSHING]
Share your tiny robot jobs and noises with us, at BrainsOn.org/contact. Can't wait to hear from you.
[UPLIFTING MUSIC PLAYING]
ANDREW: Hi, Brains On! My name is Andrew, and I live in New Westminster, BC, Canada. My colored superhero is red, and he's called Oxygenist. His superpower is he breathes in carbon dioxide and breathes out oxygen. I gave him this superpower because he will solve climate change and global warming.
SUMMER: Hi, I'm Summer, and my color superhero's color is blue. Its name is Sea Blue, and its superpowers are to control the sea.
JACK: Hi, Brains On! My name is Jack, from San Antonio, Texas. And my color superhero is Red Fire. He shoots fire out of his eyes.
AMIR: Hi, my name is Amir, and I am a 10-year-old from Zionsville, Indiana. My color-inspired superhero is named Purple Petite. Her superpower is that she can squeeze through tiny spaces. She lives in Color Kingdom, and her enemies are the Jasper Junk Food Bandits. They try to convince Color Kingdom into only eating junk food. Dun dun dun!
MOLLY BLOOM: You are listening to Brains On! from American Public Media. I'm Molly.
CYAN: And I'm Cyan.
RUBY GUTHRIE: And I'm Ruby.
MOLLY BLOOM: Hey, it's our friend Ruby Guthrie. She's here with a story about blue.
RUBY GUTHRIE: Hi, Molly. Hi, Cyan. So far, we've talked a lot about how we see colors, and what different colors mean. But have you ever wondered how you make a color?
CYAN: I have a rough idea. Usually, I think of paint, and just mixing the primary colors together. Yeah, you can create a lot of colors that way. Listeners Jonah and Kayla also had some colorful questions.
KAYLA: Hi, my name is Kayla, and I live in Davis, California.
JONAH: Hi, I'm Jonah from Ventura, California.
KAYLA: My question is, how do people make color?
JONAH: My question is, how are colors created?
RUBY GUTHRIE: Great questions. And I was curious too, so I talked to Mas Subramanian. He's a chemistry professor at Oregon State University. About 10 years ago, Mas created a color in his lab, but it happened all by accident.
[MUSIC PLAYING]
One day, Mas was in his lab, and he was mixing different chemicals, trying to create a new material for computers. He told his grad student to mix three compounds containing three elements-- yttrium, that's white, indium, which is yellow, and manganese, that's black. They took these materials and heated them up in a super hot oven. This way, all the elements could mix together to form a new compound-- kind of like when you bake a cake.
[OVEN DINGS]
But when they took it out, they were shocked.
MAS SUBRAMANIAN: I noticed that they came out stunningly blue, which I did not expect. Now, imagine my surprise, because I started with materials that were white, yellow, and black in color, and out came this brilliant blue.
RUBY GUTHRIE: Mas named it YInMn blue after the three elements, yttrium, indium, and manganese. Now, YInMn blue isn't a new color, per se, but rather a new blue pigment. A pigment is usually a powder that you use to add color to other things, like paint ink, or cloth. And civilizations have struggled for centuries trying to make blue pigments, mostly because it's such a rare color. There aren't many things that are naturally blue. And if you try to create blue with chemistry, it can be tricky to get it right.
For example, in the Renaissance period, painters used ultramarine, a pigment made from the gemstone, lapis lazuli. Ultramarine was ultra-expensive, because not only was it made from a rare material, but it also took weeks to extract the color. Since this took so much work, sometimes, ultramarine cost more than gold. So, when Mas realized he had made such a vivid blue, he put his computer work on hold to look more into his new discovery.
MAS SUBRAMANIAN: Immediately, I recognized these compounds may have a potential to be useful as blue pigment, as they are very stable. No change in color when exposed to very high temperatures.
RUBY GUTHRIE: Mas just said that this blue is really stable. That means it doesn't change much when it comes in contact with things like heat, water, or even acid. That makes it super tough and long-lasting, which is great for painting things like cars and buildings. It's so cool, literally. Not only is blue a cool-toned color, but YInMn mean blue actually deflects heat, meaning heat bounces off of it. So, it stays cool, even if it's exposed to really hot temperatures.
MAS SUBRAMANIAN: So, if you coat a building or a car with YInMn in blue, it can keep the building cooler, or the car cooler, during summertime. So, otherwise we call this as a cool pigment. So, that makes it very special, because no other blue pigment actually deflects heat.
RUBY GUTHRIE: Now, that's chilling in a freezer with sunglasses kind of cool. And to think it all started with an accident.
MAS SUBRAMANIAN: Most of the amazing discoveries come by accident. Not everything can be predicted, or never everything can be discovered by planning. I tell my students, don't think too much, just do it in the lab, and you may be able to create something interesting, actually.
RUBY GUTHRIE: Mas is totally right. A lot of times, I think, we think of accidents as bad things. But, they can actually be a really good chance for us to learn and explore. And his accident is leading to even more exploring. Mas is now trying to make a red pigment that's as stable as YInMn blue. So, keep experimenting. You never know what you might discover.
MOLLY BLOOM: Thanks, Ruby.
RUBY GUTHRIE: Thank you. And I'm off to the kitchen, I'm really craving some blueberries.
MOLLY BLOOM: All right, Cyan. Are you ready to hear the mystery sound one more time?
CYAN: Yes.
MOLLY BLOOM: OK, here it is.
[MYSTERY SOUND PLAYS]
OK, any new thoughts?
CYAN: Maybe a car backing up in the rain?
MOLLY BLOOM: Oh, good thought. Sometimes when cars back up, they make that beeping sound. Excellent thought. Well, we're going to hear it again, and this time there's a hint in the sound.
CYAN: OK.
[MYSTERY SOUND PLAYS]
SUBJECT 4: California.
[INDISTINCT]
California. California,
[INDISTINCT]
MOLLY BLOOM: OK, what do you think, now that you heard that more complete sound?
CYAN: Maybe a plane landing?
MOLLY BLOOM: Oh, yeah, because I heard the word "California" in there.
CYAN: Yeah.
MOLLY BLOOM: That's an excellent guess. Well, that is the sound of a signal at a crosswalk.
CYAN: Oh.
MOLLY BLOOM: So, you know sometimes they have those voices that talk to you while you're waiting for the crosswalk?
CYAN: Yeah.
MOLLY BLOOM: At some traffic intersections, the signals beep one way to tell you to wait, and change to a different beep when it's time to go. And that brings us back to that very important color question.
MAXIMILIAN: Why is green the go color?
MOLLY BLOOM: We asked our resident plant lover, and general green thing enthusiast, Sanden Totten, to look into this.
SANDEN TOTTEN: Oh, I love talking about green. Did you know George Washington loved the color? He called it "grateful to the eye." And studies suggest, just looking at green boosts your creativity. And right, one of green's most important roles is being the go color.
[ENGINE ROARS]
But why? I asked historian Megan Kate Nelson to weigh in.
MEGAN KATE NELSON: The green for go and the red for stop came from the railroad industry.
SANDEN TOTTEN: It turns out, stoplight inventors picked green since it worked so well for trains. But get this, originally, for trains, white was the go color. What? I know! Check it out.
[COUNTRY MUSIC PLAYS]
This was before lights ran on electricity. Back then, you didn't flick a switch or press a button to turn on a light. Oh, no. You lit a match to light a lamp. Lamps were basically teeny-tiny fires in a container. Picture a metal cylinder with a light from a fire shining through a glass window. That's a lamp. Megan Kate Nelson, our historian friend, says back then, train stations lit a plain white lamp to mean go. To mean stop, they simply covered the same lantern with a red glass cover.
MEGAN KATE NELSON: They ran into some problems when they were using white as go, because sometimes, the red glass would break, and then it would be all white.
SANDEN TOTTEN: Oof, yeah. Mixing up stop and go, that's very bad news.
MEGAN KATE NELSON: They changed it to green, so that you had a very clear difference.
SANDEN TOTTEN: That way, if the green glass broke-- which happened from time to time-- conductors would know something was up, because the light was white, not green or red. But wait, so, why did railroads pick green for go? I mean, why not purple or blue? Well, it seems like railroads chose it because factories used it.
MEGAN KATE NELSON: The very first factories that created all kinds of different objects had really big machines, and you could tell that they were on or off from the noise. But you also flipped a switch to turn them on, and that switch was often green.
SANDEN TOTTEN: Now, it's hard to find an explanation for why green was used in early factories. My friends, it's a secret loss to the green mists of time. But maybe, it was because green things rule. These factory people could have been inspired by green ferns, or green emeralds. Probably not green boogers, but maybe green parakeets? Or green algae? Or grasshoppers. Ooh, praying mantises, four-leaf clovers, three-leaf clovers, five-leaf clovers, green mold on bread. Probably not green mold. Maybe Ninja Turtles, gremlin, green mint leaves.
MOLLY BLOOM: Colors happen because of bouncing light.
CYAN: The light that bounces off of something is the color you see.
MOLLY BLOOM: Eyes take in colors with special cells called cone cells.
CYAN: Then, the brain builds a picture of what the world looks like.
MOLLY BLOOM: Red has been used as a powerful symbol in many cultures throughout history.
CYAN: People associate different colors with different feelings, depending on where they might have first experienced that color.
MOLLY BLOOM: Blue was once a really rare color pigment, but scientists are finding new ways to create it.
CYAN: Green first started to mean go in factories, then railroads, and eventually, stoplights.
MOLLY BLOOM: That's it for this episode of Brains On!
CYAN: It was produced by Menaka Wilhelm, Marc Sanchez, Sanden Totten, and Molly Bloom.
MOLLY BLOOM: We had production help from Sabby Robinson, Ruby Guthrie, and Christina Lopez, and engineering help from John Miller. Special thanks to Ladena Racine, Olivia Kuzio, Luke Burbank, Andrew Walsh, Rosie DuPont, and Libby Dinkman.
CYAN: Now, before we go, it's time for our Moment of Um--
SEVERAL VOICES: Um--
GABE: My question is, why are bees black and yellow?
DAN CARIVEAU: There's a fancy term for that. It's called aposematic coloration. And what that does is it tells predators not to eat it.
My name is Dan Cariveau. In Minnesota, I'm an assistant professor of entomology. Entomology, by the way, is the study of insects. And I look at native bees. So when we think of bees, we can think of things like a honey bee.
But in reality, there's 20,000 or more species of bees on Earth. And so we study those other bees. If you think about it, the black and the yellow, they're very high contrast in colors.
So you have this very dark black and then a very bright yellow. And what that does is it makes it very easy to see as opposed to something that might be green and drab. And so it's very easy. And what that does is it helps tell predators that, in fact, this is something you don't want to eat. It's something you don't want to touch, that really bright coloration.
There's a number of other animals that do this. So things like coral snakes or poison arrow frogs. There are butterflies that are poisonous that all look alike. And that helps them realize that the predators shouldn't eat them.
As I mentioned, there's 20,000 species of bees on Earth. And actually, most of them are not yellow and black. So we have all different colors of bees. There's greens and there's blues, and there's all sorts of browns and blacks. So go ahead and look at all the different species that are out there. They're fascinating.
TICKLED PINK: I'm Tickled Pink to read this list of names. It's time for the Brains Honor Roll. These are the amazing listeners who shared their questions, ideas, mystery sounds, drawings, and high fives with us.
[LISTING HONOR ROLL]
Brains On will be back soon with more answers to your questions.
SUBJECT: Thanks for listening.
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