yep, as stated, Ishihara is the big "net" that is mainly used to pass people and catch a few "colourblinds". If you fail this, you require further tests, the most common one being the Holmes Wright Lantern test. I believe the test is long term, not sure how it works but if you pass it, that's it. i.e. I suppose it validates whatever class medical you go for and provided you keep that medical valid, you will never have to repeat the test. I've only got a Class 2 but I've never had to do any colour vision test since obtaining it as colourblindness is genetic and you're born with it. Interestingly, it mainly affects males but can only be passed down the females in the family!
There will be new tests around, a few years ago City University developed a new one, not sure where they are with it.
A new web-based colour vision test | City University London
PS. NATS can do that test, and would do it as part of your assessment, however for peace of mind, you could also look into doing it privately in advance of any major dreams or job applications being chased.
Good Luck
CTG