Seriously, if there were more stage colors alone, I'd fire up even an otherwise vanilla version of the game on my LTO and do my best to reach them.
I have 13 colors set to show as background depending on the score achieved. The colors that do not work are white, drk green, and yellow. I currently have the colors switching every 1,000 points but that would not be a challenge enough. When should I have the background colors change? Every 5,000? It could also be something like:
Once we figure this out, I will update the game and post it.