This game is sick the concept of combining colors to change the properties of the ground is amazing! I absolutely love the puzzles the games can create with this and its a very good idea for a full game
My main problem is aiming the paint, I feel it could be easier to paint with the mouse your surrounding area, kind of like how you would place a wall in Terraria.
Something to look for is combining colors trumping other options, for example, early on: there was no reason for me not to combine yellow and blue on everything, and maybe thats intended, but it makes the answers to puzzles really simple. though maybe thats intended so its easier for the player to come up with their own solutions. Puzzles are hard to design so I can't really give much input on how you should do it. but this game surprised me