Snow White is white in the story itself - "skin as white as snow". It's a "historic" fairytale set in northern europe, where people are white. It has many adaptations, where they keep to the canon, and she's... well, white as snow. It's literally in the title.

Snow white has "skin as white as snow, lips as red as blood and hair as black as ebony". Even if she stays white, if the actress was blonde, that would bother me... she's not Snow White anymore.

I know this page is very american-centric, but snow white was one of the stories most of us here in europe read (or listened to our parents read) as kids, and we all remember the story, and the image of Snow White, we've all built in our heads.