good job! I really liked the game aesthetics, the change pallet option really adds to it, the idea is quite cool too. the only issue I found is the scaling, I'm not sure if it's even a thing in the game, I was just encountering one slime at a time and shot them no problem, the max slimes on screen never went beyond 3, but when I got to ~94 points I just got swarmed by slimes. so enemy spawner needs a bit of love.
But overall the Game is really cool! Maybe you'll check out my game too? ;)