Out of nowhere, I figured out how to simulate progressing from the beach, to the jungle, to the mountain in the game.
I am gonna use randomly generated “speckles” of playfield graphics on top of layered background colours.
What I will do is allow colours between certain vertical bands of screens up and down the map. I will just have a forward counting, non-rerversible polynomial counter for the random speckles. The playfield of course will be reflected.