Just asked my kids (Not around for the first time). One says blue and black/gray and the other said purple and green/gray. I've never known anyone who actually saw it as white and gold. Only heard that people do.
It's white/gold if you recognize that it's lit from behind. So the dress appearing darker is due to there being much less light on it than the stuff behind it.
I can't see it as blue/black because I can't make my brain ignore the fact that it's backlit. But if your brain never recognizes that, then I suppose it would look blue.