The furore began when two women disagreed over the colour of this dress. Photo / AP
It's the dress that threatened to break the internet - and apparently divided the human race into two warring factions; black/blue versus white/gold.
Experts say there appears to be no right answer, regardless of the colour of the real dress.
Watch:
Instead, the image falls into a fuzzy area on the edge of perceptual boundary; what we see is dictated by how our brain interprets light.
"I suspect the in-office and over-dinner-table arguments taking place all over the world right now are caused by each of us making a different set of internal, unconscious assumptions about the visual scene we are shown," said Associate Professor Andrew Metha from Melbourne University.
"Was this in full sun, under clouds, or maybe indoors lit by incandescent lights? Each of these conditions has a very different spectral profile - that is, the amount of different wavelengths of light.
"This issue is something our brains have to deal with all the time as we move indoors and out through different environments."
The dress debate started when two women in Scotland couldn't agree what colour the dress was. They posed the question on social media on Friday and within hours the internet was transfixed. Offices were divided, people thought their friends had gone mad and celebrities including Taylor Swift and Kim Kardashian tweeted their confusion.
Marie Rogers, a British PhD student investigating how colour word learning influences colour perception and cognition, wrote in the Guardian that the conundrum offered some insight into the philosophical question: Is your red the same as my red?
It differs from an optical illusion, where most people mistake the same thing; in this case there were two clearly defined camps.
"The brain automatically processes visual input before we consciously perceive it," wrote Rogers. "Differences in this processing between people may underlie the debate."
Stephen Westland, professor of colour science and technology at Leeds University, said there were three likely factors behind the confusion over the dress colour.
The first was due to how the image had been taken and copied.
"People are seeing the same thing on the same screen and are giving it different names. It would probably never have happened if it wasn't such a poorly washed-out set of images with poor contrast," Westland said.
The second was about what names people used to describe colours. People had three colour-sensitive photoreceptors aimed at red, blue and green parts of the visible spectrum.
Our brains could distinguish about three million colours, but we only had names for about 20 or 30 common ones, he said.
The third factor was "natural variability" in colour perception. There was about 10 or 15 per cent variation within the population, even among those who weren't colour blind.
For the record, the original dress was black and blue.
Those who judged correctly should not be too smug though, said Rogers. "Some may argue that colour itself is just a construct imposed by the brain to make sense of the world."
- Staff Reporter, Agencies
She never told them the five-course meal was vegan. So a cousin decided to act.