To make 64 colors, every pixel occupies 6 bits of a byte in RAM. The two high bits can have arbitrary values as they are masked by the pixel burst loop. This opens up all kinds of tricks. For example, they can encode play field information for a game: where there are walls, independent of their color. Here I use these bits in the snake segments: they keep track of direction so the tail can follow the head. Like invisible breadcrumbs. Up/down/right/left just needs 2 bits…
– Marcel