Is it blue and black, or is it white and gold?

One week ago, 21-year-old singer and guitarist Caitlin McNeill posted a picture of a dress on Tumblr when members of her wedding band couldn’t agree on its colors. She hoped that her followers would reach a consensus on whether the dress was black and blue or white and gold. The photo was picked up by several other news sources and ended up polarizing the Internet into two camps.

The dress, which is actually made to be blue and black, also sparked debate in the scientific community on why people see different colors while looking at the same photo.

One theory is that the discrepancy in perception results from a variation in the cones in our eyes that allow us to see colors of certain wavelenths.

Duje Tadin of the Brain and Cognitive Sciences department at the University of Rochester thinks that the number of blue photoreceptors will determine what we see.

“If you don’t have very many blue cones, you may see it as white, or if you have plenty of blue cones, you may see more blue,” Dr. Tadin said to The New York Times.

Another theory stemming from evolutionary biology attributes the variation in what people see to the way the brain processes light. According to this theory, if you perceive the dress to be in the shadow, your brain will “correct for” this fact by removing the blue tone, therefore causing you to see white and gold.

“Your brain is constantly estimating the color of the light that’s falling on the object and factoring that light out,” Opthalmology Professor Wallace Thoreson said in an interview with CNN.

Humans may have evolved this way in order to see colors both in daylight and nighttime.

“What’s happening here is your visual system is looking at this thing, and you’re trying to discount the chromatic bias of the daylight axis,” Bevil Conway, a neuroscientist, said to Wired.

A contrasting theory is that our previous experiences shape how we see things in a process known as priming.

“It could also be that you’ve seen dresses (or fabric) with the same texture or shape before, which could also affect your perception,” John Borghi, a cognitive neuroscientist at Rockefeller University, said to BuzzFeed.

Roman Originals, the company that sold the dress, has made a limited edition version in white and gold. The white and gold dress will be auctioned to support British charity Comic Relief.