I am a big fan of color-based puzzle games, so this was definitely an interesting take on the theme. The bones of what you have here are pretty solid, but could definitely take a lot of polish and design iteration. One suggestion I have is to add a button to quickly clear the current color, as it can often be difficult to tell which state the player currently is in: whether a single click will mix colors, revert to white, or just select the color as is.