Try this test and you will get a read out (a low score being best) and also a chart showing areas of the spectrum, if any, where you have difficulty distinguishing tones...
I managed 7, but considering the age of my eyes (and my monitor) I was quite pleased with that. I screen printed my test and I still can't see where I got it wrong. I have since looked at the test again but with each eye in turn and can see subtle differences. So maybe we should do the test "one-eyed".
My first score was 11 but a second try got it down to 3 :o) Didn't have to squint either. Will have to start looking at my prints twice I think, I might get better colours on them then ;o)