I had limitations on my medical for night flying and color control signals since I failed the color test given by the FAA Doc. I then had to go have an alternate test performed at one of the local universities to show that I could pass it and have the limitations taken off of my license. They don't actually send you a new medical, but instead send you a letter saying that you have passed any color vision tests that are required and that I no longer have to pass any more when I go to get my medical renewed. When I get my medical renewed, I will no longer have the limitations listed on my cert., but I will need to show the examiner the letter proving that I have satidfieds the requirements.