Thank you for that URL Giloc, I will have a read.
I think the Isihara test is largely meaningless. Most of the people who fail it are able to identify each of the colours that appears in it. They just can't make out the pattern of the number or whatever.
The lantern test is much better; you are looking at actual coloured lights.
The FAA also adds the option of demonstrated ability, where identifying real tower lights will get you a pass.
Under JAA things are a lot more rigid, with the demonstrated ability route usually being blocked for the initial medical but they do allow it on some renewals. The JAA audiogram is one example where "anything goes" on a renewal; unsuprising as so many experienced pilots are pretty deaf.
The CPL/ATPL route (where any ICAO Class 1 will take you straight in to the JAA renewal limits, so long as you have a CPL or ATPL) is going to be of interest to some people, but it is a lot of work.
I also don't think colour vision is relevant to flying. Not once one can fly a plane. The situations where colour identification is critical are exceedingly few and it's really only on tower lights (which is irrelevant unless flying non-radio) or spotting lights at night to see which way the other plane is going (very rare).