I completely agree with DaggerPen's comments. An interesting and unique concept overall.
Wow, I was all ready to come in and point out that this wasn't really very colorblind friendly, only to find your link down there. While I think it would have been ideal to include it from the start, or, as Mindraker suggested, to include a color toggle switch, but not enough people think about that, so my thanks.
In general, this is a really inventive concept. I really love seeing people build on unique game premises, and your movement is smooth, so those are both definite points in your favor. The option to speed up circling adds a lot of room for maneuvering, too, which is pretty great. I like that you have a mute option as well, though using a different key for the mute and unmute option is a bit counterintuitive.
My main issue with this game is that there's not *enough*. I don't really mind the lack of background music because I usually play on mute anyway, but this game still feels kind of... empty. This isn't the type of game to try to squeeze a story into, but the lack of power-ups or real variety beyond increasing the circling speed means that long-term play starts to get kind of monotonous.
You've got a great start and an innovative concept, but it's time to build. Add in a bit more variety - power-ups, additional balls, the ability to gain extra lives, etc. - and consider trying to add a color toggle switch into the game itself, and this could get pretty addicting.
Unique AND you even think about the colorblind people with your alternative link!
However, you could make it *even better* by just having a little "black and white" button in the game.
its a challenge that I haven't seen before, but I still find it fun. Concept is unique and creative, though simple and very easy to learn.