Colour deficiant and colour blind usually mean the same thing, however alot of people thing that colourblind means that you cannot see any colour at all. Total colourblindness is very very rare, however being colour deficiant is not, about 8% of males are colour deficiant. If you cannot pass the ishihara plates then you will usually have to pass a lantern test, although this depends very much on your authority. It sounds like you are colour deficiant and so many have trouble getting a medical for flying. check out the big thread at the top of the medical forum for lots of information about colourvision and flying.