I've been watching streams recently and the only thing that throws me off is how the animals never match their habitat. You will see vibrant colors no matter where you go, and they never look like they would actually lived there, and as some cruel science experiment an alien race dropped them off there to see how they adapted. What I would do to fix this is make its so depending on what type of planet they are spawning on give them a separate color pallet. Like say a desert planets pallet is light blue dirt, tannish sand, dark grey stone. Use those colors in the monster generation system randomly. Instead of purple green slugbeast on blue, tan, and grey, you would have a blue/ grey slugbeast. Also you could expand the pallet by adding colors associated with the habitat as well. Like say Arid/desert would have a standard pallet of: Tan, yellow, grey, black, orange, brown. This way you would get more variety, yet keep it reasonable and not allow random colors run free everywhere. Another idea to keep the colorful creatures around is when a certain animal is poisonous make it so that vibrant purple/blue/red/pink/green are in their pallet, and if they are in a jungle biome you can slap those colors in with your standard deep greens, and browns.