There's also the fact that the ability to discern two colours depends on the two shades involved, and the shades that nature presents are probably different to the ones chosen by Faber-Castell. Also, when I was a kid I could tell the purple pencil from the blue if I held them together, but had trouble if I had just one on its own. (Still true today but I don't come across colour pencils so often...)

Actually I am exactly the same. Inspired by all of this, I took an online test:

http://www.opticien-lentilles.com/daltonien_beta/new_test_da...

Which seems to suggest that I am green-blind, but not red. With 1/7 wickline, but I have no idea what that means (suspect it has been lost in translation somewhere)

This test seems to be flawed. I just did this test with four people and we all agreed that their correct solutions are sometimes wrong. Is an expert here?

Or am I color blind?

http://db.tt/0zOpPIV2

Hm, something appears to have gone very wrong there, yes. That image is not supposed to be paired with those answers.