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Are tennis balls green or yellow? They’re both, according to science

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Tennis balls are green — or so I’d thought. Which is why I was taken aback when so many people saw them as yellow, including Roger Federer, who was asked the question this week while meeting fans.

It prompted a small-scale, sports-centric version of “the dress,” with people seeing them differently, and being fervent in their response. There was no wiggle room. They were either green or yellow, and there was no in between.

Two-thirds of people see them as yellow, but this wasn’t enough. I took a photo of tennis balls into photoshop and sampled different parts of the ball. The answer seemed relatively clear: The color of a tennis ball was in between, but definitely skewed more towards green than yellow — or at least I thought.

But hey, I’m an idiot at a computer who once dipped pizza in milk and went to the wrong college. My opinion should not be trusted, so I asked someone who knows better. Dr. Mark Fairchild is the graduate director of the Color Science program at the Rochester Institute of Technology. He is an expert on color, and how people perceive it. I spoke to Fairchild about why so many people have different views on something as simple as the color of a tennis ball.

“The color of tennis balls falls on a border between colors that we would almost all agree are yellow and those that we would agree are green. I think to most, they are either a greenish-yellow or yellowish-green. However, if asked to give a single color name, yellow or green, we have no problem doing that and it sounds like the tennis balls are a color that has about a 50-50 chance of going either way … so when asked, some say ‘green’ and some say ‘yellow’.”

It’s less about the color of the tennis balls themselves, and more the color we perceive them to be. Humans, by nature, like to have definite opinions on indefinite things — leading to us firmly declaring that tennis balls are either green or yellow. But there’s more to it than that.

“There are also other variables. The lighting will have an impact and might even result in one person saying ‘green’ under one light and and ‘yellow’ under another. And then on top of that, people are just plain different. You might imagine in the extreme that a color blind person would perceive the balls differently from most. We all have small variations in our color perception that can cause colors, particularly those on a border between typical names like green and yellow to look different. It is just caused by individual differences. Just like we have different hair color, eye color, height, etc. we have slightly different color responses and that is enough to cause the tennis ball conundrum.”

This all makes sense, but surely there has to be single correct answer, right? Could we put a tennis ball into a computer and learn its scientifically accurate color?

“I could give you one … but I’d have to kill you! Seriously though, there are ways to determine one, but that would still be only in the range of observer differences, so it wouldn’t show right or wrong … everyone is right.”

Essentially we would get the color of the ball itself, but then people would just argue over what color was displayed.

“It could be measured to get a color specification, but that wouldn’t really answer the question. It would show what it is, but people could still argue over which name to assign to that specific color. In other words, we could accurately reproduce the tennis ball, but that wouldn’t answer the naming question.”

We’ve established that I’m an idiot, but I’m also an idiot who loves to be right — so I asked Fairchild if my technique of using Photoshop was sound.

“Sorry, no. First the photograph is not likely to be accurate and then you might also have some issues with the shading of the ball (parts in shadow look one color and in direct light different). I just did a Google image search on ‘tennis ball’ and there is quite a range from green to yellow and it looks like there might be a problem photographing them since they are such vivid colors. I pasted on in this email that to me shows yellowish on the illuminated side and greenish on the shadow side (light in the shadow tends to be bluish, which would make yellow look more greenish). That difference could also be causing some of the naming issues. I don’t ever recall looking at a tennis ball in person and thinking it was ‘green’.”

How to crush my confidence in one paragraph. He even used looked at the same photograph I used in my tweet. Life is pain. Why was I getting so worked up about people seeing a different color?

“Insecurity. Actually not entirely kidding there. None of us like to think we are different, but it is perfectly normal and keep in mind there is no one right answer. People vary a lot.”

Accepting defeat is part of the process, so I needed to get off this whole tennis ball thing all together. The big question, perhaps the biggest one: What is a color scientist’s favorite color?

“Red. Particularly if it were on a Ferrari (although a BMW red is quite nice, too). I’m a little bit of an outlier there. The most popular ‘favorite color’ seems to be blue.”

So, there you have it. If you said a tennis ball is green then congratulations, you’re correct. If you said a tennis ball is yellow, then congratulations, you’re correct.