I like the concept. If you do make another version you should keep a dont die mode...maybe it just takes points away or something...Also you might want to make the tank and the enemies smaller to allow for more reaction time...all in all, not bad for a 1st game.
I REALLY LOVE THIS GAME!! I hope to see a 'part 2' or more levels some time soon. Though I do have a suggestions...On the levels that can be solved with 3 colors or less, note that at the start of the level or have like a box that says the least possible # of colors...and maybe call it the challenge box or something.