Not an "F," but an "Incomplete"
Please make the colors more distinct. This is going to be unplayable for a lot of people. I'm not color BLIND, but I, and many other people, have issues with distinguishing certain colors when they're in such small and isolated pieces.
I would suggest black, white, yellow, blue and red. Green starts to confuse things, and I'm not sure if that was a brown in there or not, but brown is a really bad color for a lot of people.
Sorry, if it weren't for that I think I'd really like this game. It seems my kind of thing, but unfortunately I simply couldn't play it very far.