Steven Pinker in Forbes:
Not since the days of Mitch Ryder and Monica Lewinsky has a blue dress aroused so much passion. A Tumblr user posted this photo and pleaded “guys please help me – is this dress white and gold, or blue and black? Me and my friends can’t agree and we are freaking the f*ck out.”
She was not the only one freaking out — the puzzle has ricocheted around the internet and set off hundreds of comments and speculations, including judgments by a number of celebrities. Within minutes a dozen students in my introductory psychology course emailed me, asking for an explanation. I had to catch a plane, and at the airport bar overheard the barmaid and several patrons debating the dress. Here’s my best guess as to what’s going on.
The puzzle has nothing to do with what philosophers call the inverted-spectrum paradox (Is my red the same as your red?), which pertains to cases in which peopleagree—at least overtly—about the color they are seeing.
Nor does it have anything to do with rods and cones. The viewing conditions for the image are all well into the brightness range of the cones. The rods aren’t seeing the image at all.
And the two different percepts don’t seem to depend on the color settings of their monitor. According to the internet reports, two people can look at the same screen and still see the colors differently.
What it has to do with is lightness constancy and color constancy.