“The Many Colors of ‘the Dress’”, Karl R. Gegenfurtner, Marina Bloj, Matteo Toscani2015-05-14 (sight)⁠:

There has been an intense discussion among the public about the color of a dress, shown in a picture posted originally on Tumblr. Some people argue that they see a white dress with golden lace, while others describe the dress as blue with black lace.

Here we show that the question “what color is the dress?” has more than two answers. In fact, there is a continuum of color percepts across different observers. We measured color matches on a calibrated screen for two groups of observers who had reported different percepts of the dress.

Surprisingly, differences between the two groups arose mainly from differences in lightness, rather than chromaticity of the colors they adjusted to match the dress.

We speculate that the ambiguity arises in the case of this particular image because the distribution of colors within the dress closely matches the distribution of natural daylights. This makes it more difficult to disambiguate illumination changes from those in reflectance.