Really nice little puzzle game.  The mechanism is simple and effective and the levels are pretty good.  Hopefully you'll continue to develop this game.  A few suggestions, I couldn't find a way to restart a level when I got it wrong so I had to restart the game.  Having some kind of win reward would be nice, even you a "You solved it" message would work.  Maybe make the first few levels easier so they act almost as tutorial levels.  Great work though - keep going!