This is quite controversial, if this is an excellent game with rules I didn't get or just a top-down with different colors randomly given to enemies and ammo pickups. You need to collect color (using space button, which is unfortunately is not explained by tutorial or description) to deal damage. It seems like you lose color once you killed an enemy with wrong color, but I'm still not sure if it works that way. I also didn't understand if damage depends on what enemy you attack with what color.
I totally admit that this early prototype has a really cool idea and a great potential. Perfectly fits the theme. I like how using color mixing does kinda the same as collecting different powerups with synergies, but in a much more native and pleasant way. Good job!