I like this level idea!
If you are in the blue slope, will it be possible to roll upwards to the red again? It looks like it will not be possible and maybe that's good because then you have to really fight to stay on the red. The red area has to be small enough so it's possible to knock them off. It also has to be big enough so you don't bounce away down to the blue when you fall down. Think about what happens in donuts2 when you fall down the tunnel, you bounce away in quite high speed when you hit the ground.
Maybe it's too easy to get points because you can't fall off the map. If you get to the inner room you will either be on red or blue. And get to the inner room will be easy.