If you click on the photo you will discover a dress that was the object of much attention this winter. What colors do you see? This dress caused a stir on social networks this winter by creating two opposing groups: those who saw blue and black stripes and those who observed white and gold stripes. The debate caused so much controversy that researchers decided to try and find an explanation.

The team of Bevil Conway, a research professor at the University of Wellesley, reproduced different perceptions of color, leading to several explanations published in the review Current Biology. First, the dress is in fact blue and black, which tends to irritate the people who saw gold and white stripes. Anyone seeing it in the street or in a shop window would see blue and black stripes. If you perceive the dress in the photo in another color, it’s not the result of a neurological or visual problem. In reality, it's the way that the photo was taken which creates this anomaly, because the pixels are in fact brown and blue.

In a study of 1,400 individuals, of which 300 had never seen the dress before, researchers asked participants to describe what colors they saw, without giving a choice of two responses, which might have influenced the results. The findings were impressive, as participants were divided in two main groups, blue and black versus gold and white, corresponding to the main groups identified by social media. At the same time, a third smaller group of blue and brown was also identified. Another surprise was that differences in perception varied depending on the age and the sex of the individual. Statistically, older people and women were more likely to see a white and gold dress.

For Conway, these differences of perception can be explained by the type of light that our brain expects to see in its environment. He says that people who have just been exposed to natural light are more likely to see the white and gold dress, whereas those who are more often surrounded by artificial lighting are inclined to perceive the blue and black stripes. Finally, those who saw the blue and brown stripes are a mixture of the two previous groups being exposed to both natural and artificial light sources.

"One framework for understanding why you get these variations is to consider how light is contaminated by outside illumination, such as a blue sky or incandescent light. Your visual system has to decide whether it gets rid of the shorter, bluer wavelengths of light or the longer, redder wavelengths, and that decision may change how you see the dress," affirms Conway.