Color theory y'all.
All that yellow is molding your eyes.
I mean, just look at Miss Shipp. She's totally drowned out. Her skin is much darker but here she's on par with Miss Munn. And we've very clearly seen from other images that both Apocalypse's and Betsy's attire are NOT purple.
The background is making it look that way.
E'rybody just loooooooooooooves to hate.
And Poccy was always going to be one of the toughest villains, aesthetically speaking, to translate to live action.