>>>Please note that these are all fictional reasons, and are not based on science or reality. The idea of green skinned women is a trope commonly found in science fiction and fantasy but it is not based in reality.<<<
If it weren't in the Megillah, who would ever believe it?
Prisoners are not green. Free citizens are.
Lets the guards know what cast/zone people belong to at a glance.
It's obviously a hidden Purim message, so I'd have to go with sage.
Sage green is a gorgeous, earthy hue that may evoke feelings of wandering across a desert somewhere way out west. That high-plains drifter of a plant also lends its name to the popular herb, which gives you a hint about another meaning that this hue is associated with.
https://www.adobe.com/creativecloud/design/hub/guides/sage-green-color-guide
It's not easy bein' green. ~ Kermit
Green is the color of the emerald, a rare and precious stone even in antiquity.
It is therefor possible that makeup with a green tinge or eyeshadow would be favored by the royal femmes................