This is from the AOPA website. Notice in the 4th paragraph, they state you must take the color vision test each time you take a medical exam.
Vision—Color Restriction Removal
The medical standards in FAR Part 67 specify that applicants for all classes of medical certification have “the ability to perceive those colors necessary for the safe performance of airman duties.”
In 2002, a FedEx Boeing 727 crashed into trees on approach to Tallahassee, Fla., resulting in the loss of the aircraft and serious injuries to the three crewmembers. The NTSB investigation determined that the first officer’s color vision deficiency was one of several causal factors. As an outcome of that investigation and a subsequent safety recommendation, the FAA has modified its procedures for removing the operational restrictions for color vision deficiency. The new procedures vary depending upon the class of medical applied for or held.
If you fail the pseudoisochromatic color plate test at the time of your FAA physical exam, the aviation medical examiner (AME) may issue your medical certificate with the limitation “Not valid for night flying or color signal control.” To have the restriction removed, you may choose to take one of the FAA-approved
alternative pseudoisochromatic color plate tests. These tests take into account the degree of color vision defect and are less sensitive to mild color vision deficiency. The
Dvorine 2nd edition 15-plate test is one that you might consider taking. Your local eye care specialist, either an optometrist or ophthalmologist, may have available one or more of the allowed tests.
If you successfully complete the alternate test, you will be considered as having acceptable color vision for the FAA.
You will need to take a color vision test each time you reapply for a medical certificate. Try to take the same test that you previously passed each time you reapply. If you need to seek an outside specialist to take such a test, make sure you obtain a letter from that individual that mentions the type of color vision test and the passing results. Take this to your AME at the time of your FAA exam. The AME may then issue the new certificate without the color vision restriction.
If you cannot pass one of the alternate tests, you have another option that requires taking an operational color vision test with an FAA aviation safety inspector through the local flight standards district office (FSDO). The information describing the tests is found in
FAA Order 8900.1, FSIMS, Volume 5, Chapter 8, Sections 5-1523.F, 5-1526.E.6, and 5-1527 F.
