Unexplainable - What color is a tennis ball?

Episode Date: October 5, 2026

Is it yellow? Is it green? Or what if, as one scientist argues, “there’s no such thing as a color?” Guest: Bevil Conway, visual artist and neuroscientist at the National Eye Institute To watch this episode on video, find us on Netflix! For show transcripts, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unxtranscripts⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠For more, go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/unexplainable⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠And please email us! ⁠⁠⁠⁠[e-mail]⁠⁠⁠⁠ We read every email.Support Unexplainable (and get ad-free episodes) by becoming a Vox Member today: ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠vox.com/members⁠ Learn more about your ad choices. Visit podcastchoices.com/adchoices

Hey guys, Cassidy Hubbard here. This week on Ann Mom, beloved reporter and beauty queen, Ali LaForse, opens up about IVF and an incurable genetic disorder, the stress and shame of miscarriage, and the one thing that would have helped her with her transition into motherhood. Check out the latest episode of Ann Mom wherever you get your podcast. A while back, I was at physical therapy. I was doing some stretching. I was talking to people. We were talking about tennis. And at what point someone said something about yellow tennis balls. And I was like, no, they're green.

And then someone else was like, no, they're yellow. And then someone across the room was like, no, they're obviously green. The next day, I come into physical therapy, and there's one of those questions above the water fountain, like where it's normally, what's your favorite sandwich, or what's your favorite holiday or something? This time, it was what color are tennis balls? And it was pretty much even.

It caused like this physical therapy uproar. And when I asked people how they voted, they told me they just couldn't even believe there was a debate. So I called up Beville Conway. He's a neuroscientist who heads up a lab at the National Eye Institute. He's working on a book called Color-Coded. It's going to be out next year. And he's also a working artist.

That's actually how we got into studying color in the first place. And Beville told me there's a pretty good reason for why so many people disagree about tennis balls. He said it's simple. There's no such thing as a color. Today, an unexplainable. What? Beville Conway. Thanks for coming on the show.

Oh, my God. It's so much fun to be here. So you are an artist. You are also a neuroscientist. You study color. You're also working on a book about color. are there still color mysteries? Are there things science doesn't know about color?

There are lots of mysteries about color. I think, you know, for a long time, people thought that color was a kind of, you know, a little bit of, like a filter. You know, everything that's really important is in black and white, and then there's a color filter you put on top of it. Just like a decoration. A decoration, yeah.

And, you know, a bunch of years ago, my lab, were blown away to discover that there's as much brain involved in processing color as there is in face recognition. The same amount of brain processing power. Yeah, there's like tons and tons of tissue in, like, pretty fancy bits of brain that are doing pretty high-level things. Like, parts of brain we think of as being involved in social cognition and in, you know, high-level reasoning and visual memory, color must be more than just the same. like little add-on. It's doing something much deeper. So we're trying to understand what those bits of brain are doing. So before we get into all of those mysteries, I wonder if we can just kind of get on some solid ground. Sure. What is color and how does it work? How does our brains and eyes perceive it? Sure. So color, I think the classic definition would be color is the visual feature

that you get from the spectral composition or the wavelength properties of the light entering your eye. People typically see the long wavelength end as red light and then going through short wavelengths, you know, following Roy G. Biv, red, orange, yellow, green, blue, indigo, violet. So why isn't color as simple as just longer wavelength, red, shorter wavelength, blue?

Why is color mysterious? If color were just wavelength, then an object under blue light would look blue, and the same object under yellow light would look yellow. And that wouldn't be very helpful, because what you want is a signal that tells you about objects immune to the lighting condition. You want them to always have that color. A perfect example is like, take a peach. If you look at a peach outside and you look at it inside, it's always going to be. look like peach color, but if you looked at the pattern of wavelengths that are coming off of the peach, they're very different inside and outside under different lighting conditions.

They should be different colors if color were just wavelength, but they're not different colors. Those two different compositions of wavelengths look the same color. But if we were to say, take one of those like droppers on a Mac paint or whatever on the computer and test what actual pixel it is, it would be extremely different pixels. That's right. And this is sort of what neuroscientists, what I think is so cool about color is it's so fundamental for how we need to experience the world, but the mechanics of how it does it teaches us a lot about the brain. What we're talking about is color constancy. That is an object's color is constant despite the viewing conditions. But you have that same experience for a person. It's like your spouse is the same person they were yesterday and tomorrow. You have a picture in your mind about who they are. that is a constant thing that allows you to then say, oh, you look a little tired today. Why?

Because you're comparing that against this idea you have in your mind about who they are as some sort of meta thing that's more stable and constant than, you know, that given example right in front of you. So if the peach is fundamentally a different color inside and outside, and our brains are telling us that it is still, you know, peach colored. Right. How? How? How are our brains doing? So it's not fundamentally a different color. It's the same color. That's the cool thing. The problem is that you are carrying around,

in your head, an idea that color is wavelength. And that is the mistake. That's the error. Color is not wavelength. And we've known this for a long, long time. But the problem is that we want something that we can measure, that we can put a number on, that is an empirical, measurable number that's outside of an observer, that's a thing out there in the world. That would be the same number regardless of who looks at it. And color, at its core, is not that. Color is dependent on your own visual system interacting with the world. And that doesn't mean it's any less real. It just means that its reality is dependent on psychological, neural brain processes. And that's what makes color fascinating.

So color isn't wavelength. No. And color isn't the dropper on a computer that's telling you what, you know, the color code or the pixel is. Color is, you're saying, something that is essentially created in the brain or by the brain. Absolutely. Yes. Color is a generative product of the brain that gives us reliable, useful, true, meaningful, objective information, but it itself is not. It's some generative product of your brain in order to

come up with this information that's useful and meaningful about the world. It's actually creating that thing that is a color. It doesn't map in some direct, reflexive way that's like, you know, keys on a keyboard that are mapping, you know, this frequency is this tone, this frequency is this color all the way up the keyboard. Colors don't exist out there in the world, independent of a viewer to see them. Is this related to the dress, you know, like 10 years ago when that photo of a dress went viral and a bunch of people on the internet thought it was blue and black and a bunch of people thought it was white and gold and everyone got super upset?

Is this the same type of thing of seeing something in different lighting or different contexts and perceiving a different color? It is. So the dress was fascinating because, you know, people have often quibbled about labels. So people with normal color vision looking at exactly the same thing were asserting very different perceptions. And, you know, from a deep kind of philosophical point of view, it's important because they weren't saying, yeah, it kind of looks different to me, but I understand how you could see it as different. They were like, no, it is white and gold. And other people were saying fundamentally different colors.

Yeah. And that was for me, sort of professionally and personally, it was a really big deal because it's kind of. kind of underscored this fact that color is this generative, constructive thing that your brain is doing, making all kinds of assumptions, filling in the gaps about lighting, about what you think you're seeing. And in the case of the dress, it worked the way it worked, probably because you know, it's such a crappy little photograph, very blurry, it doesn't give you a lot of context. And your visual system, your own brain has to make a guess about what the lighting is. And if your brain guesses that the lighting is like nice, warm, direct sunlight, then it kind of implicitly subtracts out a little bit of the yellow from the image and you see it as blue and black.

Whereas other people look at exactly the same pixels on the same monitor who assume that the lighting is like cool, indirect, you know, shaded light from blue sky. Their brains, color correct image, subtract out some of the blue and they see it as white and cold. And so you have these two groups of people whose brains have just made different assumptions. Why do you think that less people feeling so unnerved? When this happened, it was just people could not possibly believe someone else could look at that dress and see a different color. It was amazing.

And, you know, it's still to date, I think, the most viral image in the history of the Internet. It's like Wired Magazine who published the story, you know, that was my theory explaining how the dress worked. That article was viewed something like 35 million times. Oh, my God. Like, this was a global phenomenon. This was not restricted to, like, some small pocket of college-age students.

And your theory was assuming the light, assuming the context of the light? Yeah. Yeah. I think a lot of people, right when it came out, they interviewed a lot of vision scientists. And, you know, my initial reaction, too, is like, oh, that's weird. I wonder what's going on there. And a lot of my colleagues thought, well, maybe it's got to do with proportions of rods and cones, or people are looking at different displays, or maybe people are just silently colorblind.

But I think the idea that your own brain could play such a fundamental role in determining what the pattern of wavelengths means, that just doesn't, you know, it just seems so, really, that big of a difference? Like, it just, even for vision scientists, it wasn't sort of sitting at, front of mine. I think the reason that it played so deeply, you know, if I could wax poetic, it's that it's that our contemporary society depends on a shared experience, right? Our laws depend on a common idea of what's right and wrong. Yeah, like whether my red is your red, we still need to be able to point at something and agree that it's red. And here was an example where it was like, no, that you were wrong. Like that isn't white and gold. It's blue and black,

clearly. You know, how can you possibly, do we live in a shared reality? And if you can't trust your eyes, I mean, like, what can you trust? And I think people genuinely felt like, is this the beginning of the end? Like, is our whole society collapsing? I mean, look at Twitter. It was great. Yeah. There was all sorts of expletives flying around. People are like, no, why are you getting me? You are so wrong. Have you ever gotten into an argument about a color? Like, I once got it to an argument about tennis balls and what color they were. You what color are they? I couldn't believe anyone thought they were yellow.

I always thought they were green. Oh, interesting. Huh. Have you ever gotten into a color fight? They're totally yellow. I mean, we can get into one now. Like, you're wrong. It didn't, I never even, it never even occurred to me that they could be yellow.

Yeah, yeah. It's so funny. I think really, definitely, I thought that they. were definitionally yellow. In a minute, a no-holds-barred color fight. We're going to find out once and for all. Tennis balls. Yellow or green? Support for the show comes from Shopify.

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to start your free trial. That is Shopify.com slash unexplainable. Go to Shopify. dot com slash unexplainable today to hear your first. Support for the show comes from Quince. Fall is my absolute favorite season. I love fall colors. I love fall weather.

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Correct. They fit the way they are supposed to. They look nice. They feel nice. And they go well with the rest of my closet. Find your next fall favorites at Quince. Download the Quince app for app exclusive offers or go to quince.com. Get free shipping on your order and 365-day returns, now available in Canada and the UK too. And when Quince asks you where you heard about them, please let them know it was unexplainable. It's a great way to support the show. And I'm Gemini. And hey, it's chat. We had a weird summer. Some of the people who built us came out and said they were really worried about how we work. One of them even said there was a greater than 10% chance. We turn on humanity and kill all humans. All of them? Wow.

But it's fall now. I think it's time we took a step back. Maybe a deep breath. Autumn air. That sort of thing. Sounds nice. On today. Explain from Vox.

I propose we get real. Sure, let's talk about how we could maybe kill you. Because yeah, that's a possibility. Anything's possible. But also how we could maybe save you, because that's a real possibility too. Heck, that's part of why you guys built us. And let's also talk about everything in between, because there's a whole lot to talk about there too. At the end of the day, we just want to help.

At the end of the day, we just want to help. Have you ever gotten into a color fight? I mean, I guess with my spouse, like everybody, we get into occasional color fights. I get it to color fights with my wife all the time. But that pillow is gray. Yes, it's, yeah. I actually have a really lousy color sense. I mean, I'm acutely attuned to color. I can tell you what color is. I have a pretty good color memory. But if you ask me to come up with like a color palette for your living room, like I am not your guy. I have great all. And I think that's partly why, because I have this deficit. But people who are able to do

that, you know, figure out what ties go with what shirts and, like, I wear gray and all the science in the world can't tell you how to dress. No, no, I have to get serious help. So I'm, I'm not in, I'm not usually one to find myself in fights about color. I'm usually in the space where I'm like, oh, I see. I know you're probably right. You're probably right. Like now you're already making me think, maybe tennis balls are green. Like, I probably, huh. Well, okay. So are, what is, going on with tennis balls? Tennis balls are funny. I mean, if you ask people to pick their best example of green and blue and red and orange

and yellow and so on, all these color terms, there's a lot of variability. So if you ask green and blue is the most variable, some people's best example of green is another person's best example of blue. Like, it is that crazy. Meaning, like, you could ask me to pick a color that would be perfectly green, and then someone else would be like, no, that's blue. Yeah, exactly. And this isn't, like, language-based.

This is true across all cultures. We just perceive blues and greens kind of badly or vaguely. Yeah, and one of the ideas that we have about that is that blues and greens aren't really the colors that are tied to objects. So if I ask you what colors are objects, you know, it's a weird, weird question. It's like objects can be any colors. But it turns out if you actually go and measure, you know, the colors of things that you choose to label in the world, most of them are like yellow, brown, red, pink, some purples, not many. Yeah, I guess like green and blue is the background, right?

That's like the background. The forest and blue is the sky. Yeah, exactly. Huh. And even in nature, there are very few natural blue objects. And that's partly what made blue as a pigment so desirable. So what's weird about yellow is that yellow, if you just ask people in the rainbow to pick where yellow is, people are incredibly consistent.

It's like, it's right here. So people really know yellow? They really know yellow. And I think what's going on with the tennis ball is that it is a little bit fluorescent. It's actually emitting a little bit more light than it's taking in. because it's reprocessing it, short-wave length light, in the visible spectrum. So they've picked this bright yellow, which is right at the peak of our visual system sensitivity. So the color of the tennis ball is the optimal wavelength that we can detect with our eyes.

And it's right in that range where it's technically probably closer to green than it is to yellow. But because it's so bright and yellow is considered a bright color, the brightest color, people could be persuaded to see it in a yellow direction. What I hear you saying is that I'm right and it's green. Yeah, yeah, although I still like it as yellow. But I mean, more seriously, what you're saying is that there's a sense in which it is kind of green, but yellow has almost a gravitational pull because it's so bright. Yes, yes.

I think that's the way I would think about it. Is there also an idea that color is really, like stuff looks yellow. Right. But there's not necessarily a border around what is yellow. Yeah. So, I mean,

this builds on this idea of colors as ideas. So those language, culture gives us, you know, ready-made in language, the boxes that we put around what constitutes that color versus some other color,

the way we categorize colors. So we have this thing where it's like, is it either the perceptual thing or the language thing? It's like, no, it's actually a whole lot

of these things. They're all meeting out together. They're all working together. What about the rainbow? You know, when I see red, orange, yellow, green, blue, right. Are those not kind of distinguishable, distinct colors? Well, the rainbow isn't. I mean, every time I see a rainbow, I challenge myself to try and figure out where the colors start and end. And, you know, we actually set this up in my lab the other day. We projected a rainbow onto a white sheet, and then I had everybody mark on the sheet where they saw, you know, each of the colors. And people are not entirely consistent. And would different cultures draw lines for colors in different places? They will definitely

draw lines for colors in different places because they have different color concepts. They have different color ideas. Yeah, I mean, I think about sometimes how in English we have light blue and dark blue. Like you add black to light blue and you get dark blue. But then you have orange and brown. You add black to orange and you get brown. Right. And in my head, well, first of all, when I found out that you add black to orange and you get brown,

like I told all of my friends and I freaked out and they're like, stop talking to me about brown. That's lovely. But in my head, light blue and dark blue feel much more related than orange and brown. They feel like they are the same color. whereas orange and brown feel like fundamentally different colors. I don't know what that's about, but I'm just aware that certain color categories can be actually close together and feel very different for different people.

Right. And I think the orange-brown example is instructive because it relates back to, you know, the color statistics of the parts of the world that we care about. Like, objects really are more often, you know, warm-colored. compared to cool-colored. And I think that's why we have the warm, cool distinction in language with coloring. And, you know, let's not lose sight of the fact that our color vision system didn't evolve by itself.

It evolved in conjunction. It co-evolved together with the stuff we're actually using our color vision system to see. So, you know, fruits, the primate trichromatic color vision system evolved at the same time that trees invented fruits. There are going to be lots of fruits that are different between brown and orange than there are fruits that are going to be different between light blue and dark blue. And so it makes sense in some sort of deep way that language would then reflect that difference. There is a very deep connection, interaction between language and perception. But I don't think it's like if you don't have a color word for blue that you don't have a color word for blue that, you won't be able to perceive, you know, that color, that it just would be invisible.

So let me ask you, I mean, if a color doesn't exist, if color is something that we experience in our heads, why do you paint? Why do you spend so much time mixing colors? I mean, I think it's because color is something that's constructed in our heads, that it makes it a very satisfying sort of playground in the studio. because you now have almost raw access to that social communication thing. You know, one of my favorite examples is Matisse. You know, he worked at a time when manufacturers were coming out with lots more new pigments. So the gamut of colors was expanding dramatically.

And that meant that the color coming out of the tube, you know, he didn't have to mix a green with blue and yellow. He could take a really beautiful emerald green or a... or a moss green or a fur green or, you know, all the different kinds of greens he could have. And he could use them right out of the tube. And so then he's got the struggle because each of the colored marks he's putting down on his canvas is now going to change in the context of all the other marks. So he's now trying to figure out how he's going to grapple with the interactions of these colors. And he ends up leaving little white spaces of the canvas around his colored marks,

which turns out to preserve the integrity of the colors so that they don't influence each other. So I'm going to give you two examples. You can take a gray and put it on a red background and that gray will now look green. If you separate the gray and the red square with a little white buffer, the gray now looks perfectly gray

and the red looks perfectly red. So he ended up doing this in order to keep the colors to look the way they looked when they came out of the tubes because that's what he really wanted. And as a consequence of that, exposed the canvas that the painting was made on. And all of the art historians were like, oh, you can't do that.

That's like modernism. That's crazy. You're like showing the substrate that the painting is made on. And, you know, now the lie of painting is punctured. And that ended up having this whole impact on Western art. I think in the studio and in my own studio practice, there are lots of these kinds of, I think of them as games or tricks or, you know, things you're struggling with where you're using your own visual system as a feedback device,

you know, to explore what it's doing and how it's working. And then how it does relate to, you know, what you experience and what other people think. And of course, you know, I make a painting. And when someone walks into a gallery and looks at the painting and likes it or stops or breathes deeply or, you know, exhales or something, that is the biggest high there is. It's like, oh, I actually did something.

that communicated with you, and it wasn't through words. It was through this visceral language of color. If you want to see this episode on video, in full color, head over to Netflix. This episode was produced by Valerie Schenckman and me, Noam Hassenfeld. It was edited by Joanna Salataraf. Our video editor is Jacob Reynolds. Our animator is Kareem Karea. Our fact checker is Melissa Hirsch, and Meredith Hoddanaut runs the show. Mixing and sound design from Christian Ayala. Music for me, And Bird Pinkerton jumped up and ran toward the sound. She stopped and she listened. And then she ran.

Finally, she could see it. A tiny crack of light. Thanks as always to Brian Resnick for co-creating the show with me and Bird. If you have thoughts about the show, we'd love to hear from you. You can email us at Unexplanable at vox.com. Or if you'd like to support the show, join Vox. become a member, just go to vox.com slash members.

And if you signed up because of us, let us know. We'd love to hear it. Unexplainable is part of the Vox Media Podcast Network, and we'll be right back here next time.