Dichromacy is a less severe form of color defect than monochromacy. Dichromats can tell some hues apart. Protanopia and deuteranopia are red-green defects. Persons with red-green defects have difficulty distinguishing between reds, greens and yellows but can discriminate between blues and yellows. Protanopes often can name red and green correctly because green looks lighter to them than red.
Males have red-green defects if they inherit a defective gene from their mother.
Affected males pass the defective gene to all of their daughters but none of their sons. Females who inherit only one defective gene are carriers of that gene. Females who inherit the gene for red-green defect from both parents are affected. Hereditary tritanopia is a blue-yellow defect. Persons with blue-yellow defects cannot see the difference between blues and yellows but can distinguish between reds and greens.