There are three types of color receptors in our eyes, red, green and blue. We also have black and white receptors. They are more sensitive than the color receptors, that is why we have poor color perception in the dark.
Color blindness comes as a result of a lack of one or more of the types of color receptors.
Most color perception defects are for red or green or both. Red-green color blindness is a result of a lack of red receptors. It is also possible to have the color receptors missing entirely, which would result in black and white vision. Check for yourself and your children for color perception defects here.