I just put my finger on why certain depictions of multiracial groups freak me out. It's because the only shows and movies that consistently feature multiracial casts are in stories that need "grit." Utopias and sweet, romantic worlds are mostly white. Nice ordinary dramas and comedies about nice ordinary people are mostly white. Dystopias, crime shows, war movies, and anything with lots of explosions are multiracial.
It's bad enough that when I see a multiracial cast, I flinch. It's not the characters themselves, and it's rarely the story; more often, it's this unspoken signal that this is a world on the edge, in breakdown, and as proof of that: Lookit! Brown people!