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What color is a tennis ball? Ask your classmates, and they might give you some 1． answers.

The Atlantic asked 30, 000 people this question. Among the people surveyed, 52 percent said tennis balls are green, 42 percent said yellow, and 6 percent said 2． else.

According to the International Tennis Federation, tennis balls 3． yellow. So, why do most people say that they’re green?

When we 4． see an object in natural light, our brains recognize its true color. Even if the object 5． in different kinds of light later, our brains can still tell its true color. 6． call this color constancy (色彩恒常性). For example, we know that China’s flag is red. When we see it during sunset or under purple light, we still know that it is red, even if it looks like a different color.

However, the color of a tennis ball is not as pure (纯的) as the flag. It appears to be a mixture of yellow, a “warm” color, and green, a “cool” color.

The US-based magazine says that when 7． brains try to figure out what color the ball is, some people ignore (忽略) cool colors like green, blue and purple. So they see the ball as yellow. 8． ignore warm colors, such as red, yellow and orange. They see the ball as green.

It is not just tennis balls that make such confusion. In 2015, a girl 9． a picture of a dress online. Some people said the dress was black and blue 10． other people said it was gold and white. They had different opinions based on whether they ignored cool or warm colors.