Hey! Great job on your game.
It's a really interesting concept. I enjoy it, but I think you could've done a better job in explaining it in the beginning, since it took me a few levels to really understand what was going on. Perhaps you could also have led in with a story? That'd be nice.
I think the thing that most people are going to be complaining about is the anti-ball. It is REALLY hard to see. In fact, I swear it disappears in some frames of the game, which makes the game quite hard to play in some of the more difficult levels.
I really enjoyed the details that you put into this game, though. That little sound you get whenever you jump, the fact that the anti-ball is the color inverse of the player's ball... they're all really cool.
I think that there could also be a level select menu. Not only would it be easier to go back and play levels you've already had fun with, but it allows you to tell other people what level you're on. For example, I'm stuck on the level that's just a black box with the goal-circle in the top right corner. It'd be a lot easier if I could just say 'Level 18' or something.
Anyways, yeah. Level select and anti-ball being more noticeable. Still, this is a seriously cool concept and I think you could easily develop this into something much bigger. Good luck in the contest!