With the MMM Mod and unique Tav, 3 (if you still use the alpha channel 4) tattoos should be possible at the same time, which can be individually colored, I mean also in metallic colors. Textures in BG3 work over the RGB + A channels and each can be assigned separate information. I use my own skin textures but I think some mods say "MMM compatible". This also allows different tattoos on different characters and I also think that it doesn't change anything in multiplayer. But yes, these tattoos have to be on one template, but then they could also be switched on/off and whether you like the tattoos is the next question.
