I'm probably missing some important point, but...

baqui63 thought this was worth mentioning said

Consider a future, within a generation or three, ie. while people from now are still alive and a functional part of society, a future where we (humans on Earth) have made contact with intelligent alien races (and not killed ourselves in the process)… Aliens that quickly become an integral part of our society. Aliens that are pretty much the same as humans… except that they have green skin.

I wonder if we will then consider it racist to have used green makeup for halloween and other costumes?

What if those aliens have fairly human-colored skin, except for green or blue eye lids? We will then say that the women of today who wear green or blue eye shadow are racist or guilty of cultural appropriation?