I really like it! At first I thought it was overly simple but then the third level showed how the game would actually be.
I am colorblind (a lot of men are and get more as they get older) the yellow and green are indistinguishable for me, I am literally not able to tell the difference between the two at all. Same thing goes for purple and blue but I can tell them apart if I stare long enough.
Otherwise, concept works! I've definitely played games like this before, but I do not remember their names.