A single photo of a dress can appear blue and black to some people but white and gold to others.

The phenomenon began on February 26, 2015, when Cecilia Bleasdale took a photo of a royal blue lace dress for a wedding. After being posted to Tumblr by Caitlin McNeill, the image sparked a global debate regarding its true colors. Neuroscientists like Bevil Conway from Wellesley College studied the image and found that human perception is heavily influenced by the assumption of the light source. This process is known as chromatic adaptation. The brain uses internal models to discount the 'noise' of ambient light. Specifically, those who perceive the dress as white and gold are often 'early birds' who spend more time in natural daylight, which has a blue bias. Conversely, 'night owls' who spend more time in artificial yellow light tend to see the dress as blue and black. A study published in the journal Current Biology in 2015 confirmed that these differences are consistent across thousands of subjects. The original dress was eventually confirmed by the retailer Roman Originals to be blue and black. This event remains one of the most significant examples of individual differences in color perception ever recorded in visual science.