I am very impressed how the 32-color Amiga version is close to the 256-color VGA version (and how much the Atari ST is lagging behind, more similar to the EGA version :)

The Amiga graphics chip had a palette of 4096 colors, you were just limited to 32 at the same time, or 64 with half bright tones, or more with chip/interrupt tricks. I doubt the latter was used on something like monkey island though.

The pirate close-up (pointed out by https://news.ycombinator.com/item?id=50495836) confirms: the Atari ST graphics are ported from the EGA version, while Amiga is based off VGA.