hello Lad's here is a very important link for anyone interested in this topic.
http://www.leftseat.com/colorvision.htm
It contains a very good downloadable article on how Colour (Color in America) Vision deficiency is dealt with by the FAA.
As we have come to expect from the americans it is a very commonsense and practical way of dealing with this issue.
Interestingly enough if you happen to pass one of the alternative tests listed by the FAA they then give you a letter certifiying that you meet the standard for colour vision which you present to the AME at all future medicals and you will never again be tested for colour vision. The same is true for the SODA (statement of demonstrated ablility) or signal light gun test, however this is the least desireable way of getting the restriction removed as it is considerd a waiver and if you apply for a professional flying job you will have to mention it on your application.
When I started learning to fly my AME gave me bad advice he sent me for the SODA straight away, I passed this test and was given an unrestricted medical right there and then, when I decided to begin my commercial training I found out about the alternative tests. I went to an eye specialist and he gave me the Devorine test and the Farnsworth Lantern test both of which I passed, The FAA then removed the waiver from my record and gave me the letter of competence. If only I had known about the alternative tests at the start it would have been a lot easier with a lot less paperwork but now that it is all sorted out, United airlines here I come.