Safe markers or any other type of paint to write spicy messages on my partners' skin?

Hi everyone... I found myself in the position of having to Dom two partner that are heavily into the Sub degradation link and I need suggestions for markers or type of paints to use on their skin. Since only one is a white Caucasian and the other a very dark chocolate skinned woman I also need colours that can stand out on dark soon like silver, white or simply non-transparent ones.

A powerful vermillion red wiild be *perfect* ...

Anyone with first hand, direct experience here can point something out? Google is marred by AI and I take my partners' well being too seriously to trust it

(Sure trusting Reddit is another can of worms but...)