How does color blindness affect the way an individual looks during a color blind test?

Loss of color vision: In the retina of your eye, there are rods (for seeing in the dark) and cones (for seeing color and fine detail). There are three types of cones, similar to the three primary colors, and the color blindness test checks subtle differences between shades to see if you are missing cones of one of the color types (usually red or green). But usually you are not aware of any problem seeing things.