Four years ago someone someone posted an overexposed photograph of a black and blue striped dress on Tumblr. It quickly became apparent that about half of us perceive the dress, not as black and blue, but white and gold.
Even before any studies had been published, psychologists and vision experts were quick to explain that the #thedress illusion is related to a process called “colour constancy” whereby your brain takes environmental lighting effects (which are ambiguous in #thedress photo), and your own past experiences, into account when interpreting the precise wavelengths it believes are being reflected off a surface.
See Christian Jarretts paper for more information
This study suggests that a color judgment can be a decision process that includes both individual perceptual experiences and beliefs about colors. Even if these two phenomena are related they sometimes differ. We found that individual differences in optimism and previous experience were related to answerability judgments about the “correct answer” to the colors of The Dress.