Here in the U.S. the governing body, the Federal Avaition Administration recognizes differing severities of color blindness. The applicant for the requisite Medical Certificate, can, after being found to have a color deficiency, request that an additional test be done. This request is always granted. The test involves identifying the colors of a signal light used by air traffic control towers in the event an aircraft's radios fail. The colors are, individually, green, red and white. Most applicants have no problem with red, but often have difficulty defining green from white. The test should be done at dusk for better deffintion. In my experience, about 70% pass the test. Granted, the military applicants are subject to different standards, since they don't have to take any and all applicants...