While most of us can see the wide variety of colors in the world, some people see only shades of gray. If you have normal color vision, you are a trichromat , and if you can see only light and dark, you are totally color-blind, or a monochromat . It is more common to be partially color-blind, or a dichromat .
Color blindness is determined genetically, is sex-linked, and occurs mostly in males.
The dichromat lacks one of the three types of cones. For example, if the red-green complement of cones is missing, he will be unable to distinguish red and green and will see all colors as yellow or blue. Among men, about 7 percent of the population suffers from red-green color blindness. A few individuals have blue-yellow blindness and see all colors as red or green . Although many animals , including dogs, are monochromats, there are very few cases of total color blindness in humans.