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

US magazine The Atlantic recently asked 30,000 people this question. Among them, 52 percent said tennis balls are green, 42 percent said they are yellow, and 6 percent went with other colors. According to the International Tennis Federation, tennis balls are yellow. 【小题1】

Scientists 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. 【小题2】 Even if the object is seen in different kinds of light later, our brain can still tell its true color.

【小题3】 It appears to be a combination of yellow, a ''warm'' color and green, a ''cool'' color.

According to The Atlantic, when our brains try to figure out what color the ball is, some people ignore ''cool'' colors, such as green, blue and purple. So they see the ball as being yellow.【小题4】 They see the ball as being green.

【小题5】 In 2015, a girl posted a picture of a dress online. Some people believed the dress was black and blue—but others thought it was gold and white. They had different opinions based on whether they ignored ''cold'' or ''warm'' colors.