This passage is about color blindness and why people are color-blind.
Do you know any color-blind people? One percent of the population of men is color-blind. They can still see some colors. They often can't tell two colors apart. Usually red, green, and yellow look the same. Sometimes it's blue and yellow. People are born this way. The back part of the eye is called the retina. It has many little cells. They sense light. Some sense specific colors. These are called cones. Cones sense red, green, and blue. Sometimes one color of cones just doesn't work. Then a person cannot see that color. Color blindness makes driving hard. A color-blind person cannot tell a green light from a red light. They don't know whether to stop or go. So they have to remember the positions of the lights. A bouquet of red roses must look strange. They can't tell the petals from the leaves.