I was actually planning on making a game with this exact concept!! Then i decided it'd be too hard to get enough in within the 72 hour time limit. Well done on getting something done that is actually decent! I would have loved to see power-ups that help the player and also hinder the competition. When I was thinking of this conception I was thinking of 'blobs' that run around an arena leaving trails of slime in their colour and you have to run around and shoot them with paint (or something) to turn them your colour.
The concept is really sound I just think it needs more than just turning as much of the ground your colour to work well.