Is the dress blue-and-black or white-and-gold?
Interestingly, when I first saw the photo it was clearly white-and-gold. However, looking at it again 30 mins later it appeared blue-and-black.
I suspect it has to do with how we internally white balance the photo. We quickly interpret the light area of the dress as either "blue" or "white" and everything else then follows (the dark area will either be black or gold respectively). It's hard to change that choice at will, so we're convinced of our interpretation.
And, for what it's worth, in reality the dress is likely blue and black, but I don't think that matters since we could have set up an identical shot using a white-and-gold dress and a different light bulb instead. www.amazon.co.uk/Roman-Womens-Detail-Bodycon-Dress/dp/B00SJEUIME
[Via twitter and recent news stories]