Human beings need to be able to see color. For instance, it is an important cue for detecting motion. This may have evolved from the need for early humans to be able to spot a moving predator hidden in a dense forest. It's also important for perceiving shape. Shape is defined by the edges and color changes at the borders of objects.
But how do we actually "see" color? The secret is visible light, which is made up of a spectrum of colors that the human eye can identify: violet, indigo, blue, green, yellow, orange and red. There are three types of color-receptors in the eye. These color receptors are each sensitive to a particular wavelength, or color, of light: green, for example, or red. These three primary colors in light can mix in the eye. This enables us to see more complex shades of color, such as violet or orange.
When sunlight, for example, shines on a bright red apple, the apple's surface absorbs all the rays except for the red ones. So a red ray of light is reflected to the eye. The eye receives this red light and sends a message to the brain. The brain then deciphers this message, and associates it with a given color. Researchers have even pinpointed the part of the brain that controls the conscious experience of color. It lies near the back, behind and below the temples.