In the beginning there was a dress. This dress was photographed and put on the Internet, like many dresses before it. That’s where things got messy. This particular dress was particularly confusing because to some it appears blue and black, while to others, it is clearly white and gold. What began was a debate for the ages. It implicated God and man and the cosmos.
Here's one of the Tumblr posts that really got the argument going.
For the record, the dress appears to be, in reality, a black and blue item from a shop called Roman.
BuzzFeed’s Claudia Koerner, meanwhile, unearthed the origin of the picture—in Scotland. A “bride and groom couldn’t decide if the dress was blue and black or white and gold… So they posted the photo on Facebook,” according to BuzzFeed, where you can check out the full yarn.
Why do some people see the dress as white and gold while others see it as blue and black? (Some people even see it both ways, seemingly at random.) The informed consensus seems to be that it has to do with psychology/vision issues related to the brain's natural process for adjusting to varying lighting conditions; Wired posted one of the earliest clear explanations of that theory, and Pascal Wallisch wrote about it for Slate. (Though it should be noted that what was most amazing and engaging about the Great Dress Debate was just how long it went on without any explanation at all surfacing. For hours, it just seemed like strange magic, or a prank that everyone else in the world was surreally in on except you.) From Wired:
Without you having to worry about it, your brain figures out what color light is bouncing off the thing your eyes are looking at, and essentially subtracts that color from the “real” color of the object … Usually that system works just fine. This image, though, hits some kind of perceptual boundary.
It's worth noting that this emergent theory still doen't really explain are so many differences between specific individuals' perception. Why does this one image confound and divide people who see other colors the same way, who live in the same location under the same sunlight conditions, who are looking at the same screen from the same angle? The story of the dress is still developing.
Update, Feb. 27, 2015: This post has been revised for clarity.