Want to test your ability to discern colours? FM 100 Hue Test is a very hard way to check how good or bad you are (or how good or bad your screen is :p) arranging four strips of different colour hues correctly.

I must say I thought I'd get a perfect score (ZERO!) but I got a 12... The ones I did worse on were the bottom two so my advice is to not do the whole thing in a row because it's really hard on the eyes.

Good luck!