Defiantly a fun and easy to play game! however a few complaints I think as far as the theme goes. Using Alpha to fade your particles away breaks the Emerson of gameboyness the game had going for it. This also introduced another problem and that was showing more then 4 colors. I think you would have been just fine ending the particle without any alpha applied.
Not being able to unmute audio during gameplay was a bit odd of a choice. I think if you are going to have sound controls within your game they should be the same throughout the game. Assigning a key to M to be able to globally mute audio at any time would have been nice.