So I tried out KoalaPaint (for the Atari 8-bit computers) today, and it seems like the entire picture could only have 4 colours at a given time? (unless you're doing rainbow mode)
Cause when I tried to change the colour on the palette thing then the same colour on the picture also changes. Also, i haven't figured out how to make multiple pictures yet (it's probably in the manual but I haven't gotten round to reading it fully yet). Unsure if you could do an extra 4 colours in a second pic and the "copy" it to another picture, creating up to 8 colours, though I doubt it, looking at some Koala art.