Rods , which provide vision in dim light, have no ability to distinguish between colors. Cones are responsible for color vision. There are three different types of come pigment in the normal eye. Color vision occurs within the visual part of the brain compares electrical signals from the different types of cones. Defects in color vision are either inherited or acquired.
Inherited defects result mainly from missing or incorrect visual pigments.
There are different types of inherited defects, with different levels of severity. Color vision defects sometimes can be acquired, as a result of eye disease or normal aging or as a side effect of certain medications. In acquired defects, other parts of the eye besides cones and cone pigments may be affected. Inherited blue-yellow defects are rare in either sex. They see only different degrees of lightness.