Very creative idea, I like that both balls have different mechanics. However, it was a bit too easy to just keep the the white ball sinked and avoid all obstacles, as the black ball doesn't get half as many. If you want to develop this further, maybe you could make it so that the score rises faster if you keep both balls together, that would force the player to take more risks.
Still, great idea and very well implemented, the game is so elegant! Great job!