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What color is a tennis ball?

A neuroscientist and artist argue there’s no such thing as a color.

A while back, I was at physical therapy, and the topic of tennis came up. Someone said something about yellow tennis balls, and I was like… “What? They’re green.” And then someone else chimed in, “No, they’re yellow!” And then someone across the room hollered, “No, they’re obviously green.”

There was basically a physical therapy uproar. And when I started asking other people how they saw them — yellow or green — they told me they couldn’t even believe there was a debate. So I called up Bevil Conway. He’s a neuroscientist who heads up a lab at the National Eye Institute. He’s working on a book called Color Coded, which is due out next year. And he’s also a working artist — which is actually how he got into studying color in the first place.

Conway 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.”

In the latest episode of Unexplainable, I talked with Conway about what color even is, the viral dress fight (black and blue or white and gold?), and why we get so upset when people don’t see color the same way we do. Below is an excerpt of our conversation, edited for length and clarity. Listen to the episode anywhere you get your podcasts or you can watch on Netflix.

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. For a long time, people thought that color was a little bit like a filter, that everything that’s really important is in black and white, and then there’s a color filter you put on top of it.

But 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 processing power?

Yeah, there’s tons and tons of tissue [and] pretty fancy bits of brain that are doing pretty high-level things — parts of brain we think of as being involved in social cognition and in high-level reasoning and visual memory. Color must be more than just this little add-on. It’s doing something much deeper. So we’re trying to understand what those bits of brain are doing.

So what is color? How does it work? How do our brains and eyes perceive it?

The classic definition would be: Color is the visual feature that you get from 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 ROYGBIV: red, orange, yellow, green, blue, indigo, violet.

If color were just wavelength,........

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