Kids usually begin to identify colors by age 3 or 4.  A 4 year old child who can identify some but not all colors might be normal, but it’s worth knowing if he has a physical impairment in recognizing colors.  He’ll be frustrated if the adults try to teach him something that he might be physically incapable of learning!

Red-Green color blindness is the most common type, but Blue-Yellow color blindness also occurs; about 20 different types of color blindness have been described.  Several genetic types exist; Wikipedia has a very complete description. Most color-blind people are male, but some females also suffer from it.

A person who has Red-Green colorblindness sees red and green as the same hue.  He can tell the difference between dark red and light red, but red and green colors of the same intensity both look gray.  Other colors (such as olive-green and brown) might also be hard to distinguish.  This is a minor inconvenience most of the time, but it can cause a safety problem on occasion.  (Traffic signals are always arranged with red on the top, for the benefit of color blind drivers and pedestrians.)  It is not true that everything looks black-and-white to color blind people; they can see many different colors, but not quite as many as a person with normal color sight.

Simple tests are available.  On-line screens, like this one (good for younger kids who can identify shapes) or this one (good for kids who can identify numbers), can give  you an indication of color blindness; but if your computer screen doesn’t have perfect color rendition, the test might be thrown off.

–  Copyright 2009, David M. Epstein MD