Color blindness, also called color vision deficiency, is a condition in which a person has trouble differentiating between certain colors.The main reason behind this problem is that the cones of one's retina are defective.

The most common type of color blindness is the inability to distinguish between red and green, but some people cannot tell blue and yellow apart, and very rarely a person is completely color-blind, meaning that they cannot see any colors at all.

Color blindness is genetically inherited, and it is more likely for men to inherit it, due to it being linked to the X-chromosome, though it can be acquired later in life due to various eye conditions, diseases, or medications.

People who suffer from color blindness rarely have trouble with anything else aside from the colors themselves, and most can learn to compensate for their deficiency, using other cues like brightness, position, or symbols.