How Many Colors Can Humans See?

There are an estimated 10 million color hues that humans can see. The human eye has three cones, each of which is able to view either red, green or blue. All of the other colors that humans can see are referred to as secondary colors and are created by combinations of these primary colors. It generally is believed that the human eye cannot see red-green or yellow-blue, referred to as the forbidden colors, because each color in the pair takes different actions in the brain that cancel out each other.

More about color vision:

• The most fatiguing color to the eye is thought to be bright pure yellow, because the color reflects the most light and thus causes the most stimulation of the eye.
• Chickens that are exposed to red light are less aggressive, studies show, although it is not known why this happens.
• In 2010, researchers found the first confirmed tetrachromat — a person who has four cones in the eye instead of three, and who might be able to view hundreds of millions of colors.