Not entirely true it was only the white skin, she also had black hair and very red lips.I've always seen it as her uniqueness that was considered attractive, not particularly her skin.

Black hair is not a typical trait of people who have very white skin, I guess you could have a similar story about a dark skinned woman with fair hair.But that would not be an image the Brothers Grimm readers would as easily imagine in their heads, and would be more likely for a story written somewhere where that would be more likely and identifiable.

Aren't there African stories that have beauty standards about being as black as a black stone?