Obviously there's only so much you can fit into a game jam (and I gather from the replies here you were probably shorter on time than most), but a little more audio would have done wonders here. Just a little victory jingle, even. Still, it's an impressively solid game as far as it goes: the timer, and the possibility of, say, moving Yellow to the heart before spotting the switch necessary to free Blue on the third level is an effective combination. I imagine you could come up with a bunch more interesting levels if you wanted to expand it.