Sorry about joining this thread a bit late, but thought the following might
be of interest;

for one thing, here is a pretty good reference should you want to know
about colour vision and aviation, from an Australian AME named Dr Pape:

http://www.aopa.com.au/aviation/colourvision.html

Note that I would suggest you get in touch with your local AOPA chapter,
they should be able to direct you to the most up to date information
relevant to your own neck of the wood (and, should a career in aviation
is really important to you, you can always emmigrate just like I did);

Although our friends down under seem to be the most advanced on this
issue, the USA FAA has a pretty pragmatic approach, and it essentially
works as follows: should you fail the run of the mill Ishihara test that
your local AME is most likely to use, you can try to pass one of the
FAA approved alternative (list available from AOPA or your friendly local
FAA office), e.g., Farnsworth D15, etc. The neat thing about these
alternative tests is that you can fail them as often as it takes you to
get one right; then you are set for life. Should you fail this, you
can apply for an actual light gun test; you take your first during
daylight; should you fail this test you can take it one more time at
night... (and if you fail this one again, you are stuck with the restriction
for good, hence the value of going for the approved alternative tests
first);

I got mine right at the second (night) attempt... :-/

I now have a neat letter saying that I passed the thing, valid for
all classes of medical and for life. I present it to the AME everytime
I renew my medical.

i.e., I can now happily fly at night under my FAA certificate, but
not under my (pre-JAR) British PPL(A); the laws of physics being evidently
different on either side of the pond. (Note that in the whole history
of aviation, there hasn't been any accident or incident ever reported that
was ever connected directly or indirectly to colour vision defficiency, but
I digress.)

--Sylvain