HAM-like hack allows full-color GIFs

[minator]

No, HAM uses extra bits to change the colour value of a pixel.

This uses multiple images to generate the illusion of more colours, you could do this on the Amiga as well, I was experimenting with it in DPaint on an A1200 many years ago.

[minator]

It's a hack in that it allows the file to represent an image with more than 256 colours, not display more than that many on an 8-bit display.

As such, it wouldn't work on a 256 colour screen.

No, thats the point, it does allow >256 colours even on a 256 colour screen.

The screen itself only displays 256 colours at a time but your brain will combine the frames so you will "see" a different image with more colours.