From my quick accidental experiment, I think that what you see is related to your visual experience in the preceding minutes.

I too was looking at this and thinking, "How can anyone say that that dress looks white and gold?" I could only see blue and black.

I went outside to get lunch, came back, got yet another dress picture in my social feed but lo, it was white and gold...!

My immediate assumption was that I had seen a doctored image but having gone back to this post, where I previously could only see blue and black, I could now only see white and gold.

My hypothesis is therefore that the type of light you've recently been experiencing influences how your brain interprets the colours in the dress image.

Going from daylight into artificial fluorescent lighting gives White/Gold. But, after some time under fluorescent lighting it turns Blue/Black. For me this hypothesis is somewhat supported by the fact that now that I've been back inside for 20 minutes the dress is Blue/Black again.