What color is a tennis ball? Ask your classmates, and they might give you some surprising 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 something else. According to the International Tennis Federation, tennis balls are yellow. So, why do most people say that they’re green?

When we first see an object in pure (纯的) color in natural light, our brains can tell its true color. Even if the object is seen in different kinds of light later, our brains can still tell is true color. 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, it looks like a different color. However, we still know that it is red.

However, the color of a tennis ball is not as pure as the flag. It appears to be a mix of yellow, a “warm” color, and green, a “cool” color. The US-based magazine says that when our brains try to tell what color the ball is, some people can’t notice cool colors like green, blue and purple. So they see the ball as yellow. Others can’t notice warm colors, such as red, yellow and orange. They see the ball as green.

It is not just tennis balls that make such confusion (混淆). In 2015, a girl posted a picture of a dress online. Some people said the dress was black and blue while others said it was gold and white. They had different opinions based on whether they just noticed cool or warm colors.

In our life, we can see colors everywhere. Some colors make us feel relaxed and peaceful while others make us feel upset and nervous. Scientists have studied colors and feelings for a long time. Many believe that colors can make a difference to our feelings.

Warm, bright colors such as yellow and red positive (积极的) colors. They can give people a pleasant feeling. Cool colors such as blue, purple, and green are relaxing colors. They help people have peaceful feelings.

Orange makes people feel hungry, so many restaurants are painted in this color. Blue is a peaceful color. It helps people rest, so it is a very good color for a bedroom. Green means new life, so sick people need this color to make themselves feel better.

However, colors can cause bad feelings, too. Some types of blue make people feel sad. Red can make people full of strong feelings. People may become impatient (没有耐心的) or even get angry more easily because of it.

How do you feel right now? Now look at the color of the walls around you. Does it match your feeling?

Hello，I ________ Alice.   这是一个杯子。It   ________blue.That is a key.It's blue, too (也).   pen，a，this，black，is. And that's a green quilt.It's good.