I spent awhile gathering the best compenium and concept art images from the ultima manuals I could find. Then I used IrfanView to batch scale them all to the same size, then I used Free Texture Packer to generate an atlas. Then just took the Ultima VI bestiary images, originally in black ink on white, and I adjusted and colored them considering the in-game graphics from Ultima VI for each entity.
This is part of my Age Of Singularity project, where I'm re-creating Ultima VI in Unity. It's also part of my bigger attempt to understand big fantasy bestiaries, and I've done some similar coloring for my #ProjectUltradeep DnD Forgotten Realms / Waterdeep / Undermountain project. Some things are interpretations trying to reconcile the artwork with the in-game sprites; I gave the troll black hair and yellow horns, but I'm not sure if that's right, for example.
I know the original palette was limited due to the VGA graphics, but I hope to retain the vibrancy of the Ultima VI classic with my models and textures.
Here's the original fb UDIC post.