The first time I heard this, it came from one of the Dirty Harry movies.
Eastwood gets out of his car in a bad neighborhood. There’s a gang of black youths standing around, and they offer to watch the car for him. It’s obvious they’re screwing with him. To show them he’s a real badass, he responds with, “Well, that’s mighty white of ya.”
So, yeah, I’d have to say that it’s definitely a racist remark; probably meant to show that white people are real dependable, stand-up folks, while black people can’t be trusted and are basically lazy, undependable bums.
I hope to shout that I am not construed as a racist in the above post.
And the problem with small furry animals
in corners is that, just occasionally,
one of them’s a mongoose.
Terry Pratchett, Witches Abroad