Cool concept, I especially like how visually appealing it is, despite the very simple appearance at first. The sort of spilled-paint-ink-thing effect when you win is great, is it some kind of well executed standard animation or something more sophisticated?
My one criticism would definitely be dying by touching the edges. I don't even think it's about the edges being hard to see (though that doesn't help). I believe it shouldn't happen period, you should just stay at the edge until some other color shift kills you. Dying to the game window feels kind of cheap to me, like dying from some arbitrary limitation and not from game mechanics.