A person with normal color vision can typically perceive up to 1 million different shades of colors. Normal color-sighted individuals are Trichromats, meaning that have three different color sensitive cones in their retina: red, green, and blue. Each of these red, blue, and green cones are sensitive to different wavelengths of light and help to create color perception. The unique separation and overlap work together to enable those with normal color vision to see all the colors of the spectrum.

The red, green, and blue color sensitive cones of a person born with color vision deficiency are positioned in such a way that there is less separation between them and an excessive overlap. This reduces the shades of colors seen and the brightness of color, compromising the perception of many colors. As a result, it is believed that a person with typical red-green color blindness often perceive only 10% as many shades of color as a person with normal color vision. Read more about types of color blindness.