Most of the blue dress explanations are that its appearance depends on whether you think it is in the dark or in the light. Some anecdotal evidence for this is that I see the dress as gold and white and my friend Celine Harvard told me to stare at a light and then look at the dress and I was able to see it as blue. But what are the subtle cues that cause different people to see different things? I don't know.
However, I today saw a nice illustration on twitter that is making the rounds of a perception mailing list that do convince me of the mechanism if not what cues are at work:
The right hand of each dress are the same physical colors. So the implied lighting carries the day.