Nice concept, but needs improvement. Keeping it in one level that is bound to end is some sort of a turn off. Look at AA more, see how they change the mechanics in levels in a simple manner (changing speed, direction, etc...).
Colors is an interesting concept, I think you can play with that, and you can play with the circle size: maybe make it grow and shrink at certain levels?
Ya36eek il3afiyeh :)