What Color Is 'The Dress?' Visual Perception Expert Explains the Debate

On Feb. 26, a single image of a dress sparked a debate that swept across the Internet. The population was divided: was the dress white and gold or blue and black? While some saw one set of colors, others saw the other set--and no one could agree. Now, an expert on visual perception has taken the time to explain the mystery of the dress.

"A couple of things are going on, and not all of them involve how our eyes and brains see color," said James Promerantz, a professor of psychology at Rice University and an expert on visual perception, in a news release. "As people who have studied visual perception or photography or painting know, there is a problem that eyes and cameras struggle with called 'white balance.' If you look at your camera closely, there may even be a white-balance control on it that makes this setting for you."

For example, in the picture above, the checkerboard square marked A is identical in brightness to the one marked B, even though B looks far lighter.

"The reason we see them as different is that we factor in the obvious shadow being cast by the cylinder, blocking the source of light pouring in from the upper right," said Pomerantz. "Because B is in shadow, we must mentally (albeit unconsciously) correct for it being in the shadow. A camera doesn't know about any shadow or any cylinder or any light streaming in from the upper right. All the camera knows is the brightness at each point (pixel) in the image, and so the camera sees A and B as identical."

This same idea extends to the color of the dress. We can't tell the difference between white and blue, or between black and gold, unless we have some independent information about wavelengths illuminating the dress.

"What's correct is that the dress itself, which is for sale online, is actually blue," said Pomerantz. "That means that the lighting under which the photograph was taken must have been a fairly good white-that is, an event mixture of all wavelengths or colors-and thus a flat spectrum."

In other words, it all has to do with how we perceive light and color. While the dress may actually be blue, the fact that most people see it as white and gold isn't surprising.