Alberto, you might want to check the extremely long thread on colour vision. There isn't much that isn't in there. But yes, I believe that once you've passed a colour vision test you won't be tested again as it's considered to be something that does not improve or worsen with age.
The whole JAA concept and application of colour vision testing is a farce anyway. If a doctor was to test patients in breach of procedure like JAA test pilots for colour vision, they'd be struck off! It's flawed, discriminatory, and you might just find something brings a very well researched legal challenge forth in the not too distant future...