It's true. If the image you pick as been compressed or modified, the number of colors is CHANGED !
That's why galahad find 1082 colors. an uncompressed screen shot taken with winuae
with no artifacts give between 85-107 more or less.
HOL screenshots are not LOSSY screens, they are modified !
Risky woods is 64 colors as stated in the credits, with a big use of copper.