Do those people who see it as black and blue have color blindness of some kind? It's quite clearly brown and blue-gray to me. The eye dropper in Paint.Net says the same thing. Not sure how anyone can get black out of this.
I interpret it as black getting colored colored brownish by the camera/lighting. Specifically, if you look on the left you can see another dress which seems to be black/white. And in that area, the lace appears the same color as the black of that dress.
That's exactly it. It's a low-light photo, so colors are distorted. In addition, it looks as though the in the photo is on the yellow/orange side of the spectrum, washing out the blue to make it look white.