A photograph goes viral
On February 26, 2015, a photograph of a dress ignited a global debate. Posted on Tumblr, the image showed a garment that some people saw as white and gold, while others insisted it was blue and black. Within days, the post generated millions of tweets and over 37 million views on BuzzFeed, as viewers argued about the dress's true colors. The manufacturer, Roman Originals, later confirmed the actual dress was royal blue and black.
The intense public disagreement was a unique case study for vision scientists. The phenomenon shows a principle of visual perception called color constancy. This is the process by which the human brain adjusts its perception of an object's color to keep it looking consistent under different lighting conditions. The photograph that went viral was overexposed and had poor white balance, creating ambiguity about the light source. This lack of information forced people's brains to make assumptions, leading to starkly different perceptions of the same image.
Your brain's unconscious guess
The scientific explanation for the illusion is connected to Wellesley College, where neuroscientist Bevil Conway conducted one of the first major studies on the phenomenon. Research shows the different perceptions arise from unconscious assumptions about the lighting in the photograph.
If your brain assumes the dress is in a shadow and lit by bluish daylight, it automatically subtracts the blue wavelengths of light. This mental correction causes you to perceive the dress as white and gold. Conversely, if your brain assumes the dress is under yellowish artificial light, it subtracts the longer, yellower wavelengths. This leads you to see the dress in its actual colors: blue and black.
A study published in Current Biology surveyed 1,400 people and found that 57% perceived the dress as blue and black, 30% saw it as white and gold, and 11% reported seeing blue and brown. Further research suggested a link between a person's typical light exposure and their perception. People who identified as "larks," or early risers accustomed to natural daylight, were more likely to see the dress as white and gold. "Owls," who are more accustomed to artificial light, were more likely to see it as blue and black.