The art style was simple but great and I liked the overall idea. Got very hard though! I couldn't manage the level with reds and blues each having the three rock stack. Makes me think I might have missed some trick to the game.
I recorded myself playing, the video is here if you want to see:
https://www.youtube.com/watch?v=9yGg3lucYHM&index=17&list=PLdLeOxRHtRXoFhBNnWybP1VhJ6jYGiIO5