Color

Well that was boring. There's no challenge in this game. You can't die, no matter how may times you're hit. You can kill all the enemies just by holding the up and left keys the entire time. And the only rewards are occasional palette swaps and a trite 'story'.

Each colour should have different power.
Laser, bombs, bullets, rockets, soundwave etc.

I've updated the game, now there is more challenge and music =)

Thanks for the comments :) , I was more focusing on the atmosphere/little story than to really make it a hard and competitive game

Everything Chaotic Brian said is true. As a note to the dev as to what you should do next time. Limit the number of bullets, lessen the number of enemies, make getting hit mean something, and make the enemies bigger targets.