A reduced ability to tell the difference between certain colors.

Color blindness is a reduced ability to distinguish between certain colors, usually shades of red and green. The condition often runs in families. More men than women are affected. Other causes include certain eye diseases and medicines.

Color blindness can be mild, moderate or severe. In the most common type of color blindness, it's hard to see some shades of red and green. For some people, it's hard to tell the difference between shades of blue and yellow. For others, everything appears to be a shade of gray.

In some people, treatment of underlying conditions can help color blindness.