Very fun! I wish it wasn't so easy to lose though. =P
a "# of moves left" counter and a difficulty setting and this game is instantly in my book of awesome time-waster puzzles. It's more fun than Sudoku.
There actually is a difficulty setting, I just have it set manually for the time being. I can look into adding the moves left counter when I end up updating it again (I'm going to try to figure out an algorithm to make a puzzle always solvable in x moves, then I plan to update it again).
[edit for my own reference: there's currently a bug where if you start another colored move before the previous one finishes, it doesn't transition properly]
I did end up reporting this as a bug, but apparently it's not a bug.