If you have physics mod and use the ragdolls spiders and creepers etc will first bleed their usual color like green then after they will bleed red. This is with only ragdoll and not ragdoll blood on mob settings with physics mod. Iron golem and skeletons will also bleed. Idk if it matters but I have physics mod pro (which is free but on the patreon if you scroll all the way down) but idk if it matters.
Turning off ragdolls fix this but I'd like to keep them. Great mod other than this!

Edit: Forgot to say, forge 1.20.1

Hm, and when they bleed the different colors is it the blood from the physics mod or my mod as I know the physics mod has its own blood particle system in place. I'm releasing a new version of my mod that should play nicer with it, but I'll check on this as with the new version too.