Originally Posted by mc6809e
But if a programmer really wanted to he could page flip and use the COPPER to alter the 16 palette registers of a HAM image mid-scanline to improve it further. I think during HAM display the COPPER can perform 35 arbitrary writes to the 16 color palette available in HAM.
This is called Sliced HAM (SHAM). Newtek Demo Reel 1 (1987) showed this off in a hires interlaced imagine.
EDIT: The Netwek image wasn't actually HAM, now I come to look it up. You could do interlaced HAM but not HiRes. It did use palette changing trick though.
I wonder if originally the idea came from the old arcade machines that used a monochrome screen with a coloured filter on top.