When one of the three cones does not function at all or is missing, the most severe color blindness occurs. Those defects are classified into Protanopia, Deuteranopia, or Tritanopia according to whether the defective cone is L-cone, M-cone, or S-cone respectively. Additionally, when the spectral sensitivity property of either L-cone or M-cone is the intermediate between them, the slight or moderate color deficiency occurs. Those are usually due to heredity, and about 8% of males and 0.5% of females have some degree of color-vision deficiency in Europe and America.

The following are the simulation images of how the color patches appear to protanope, deuteranope, and tritanope. However, those are not so accurate because of the difference between each of the monitor's characteristics. (You can also watch the color blindness simulation video1 and video2.)