CAA Computer Test
Add me to the list that failed Ishihara test, but passed at the CAA.
I took the computer based test there last year. It takes about about an hour, and comes up with an incredibly accurate description of your colour response in both axes. The idea behind the CAA test is that (for red-green at least) they figured out an empirical point beyond which you start to lose the ability to read the PAPIs, and set that as the limit.
So a good rough guide is: if you can read PAPIs, then you will probably pass the CAA test.
I normally manage about 4 out of 16 on the Ishihara test, but I was well within the CAA limits.