What color is the dress? I can see both. I'm pretty sure there are a couple of effects going on, but i can look at it and have it change like the old woman-young woman optical illusion. I suspect there's something going on with color and brightness constanciesin that the dress is unfamiliar (and perhaps ugly), the lighting around it is ambiguous, and one can "read" the photo as the white and gold dress in the shade with a bright background or a blue and black dress over-lit under harsh lighting.
This is also posted at http://elainegrey.dreamwidth.org/551928.html .