It was one of the most fractious debates in modern times – by 2015’s standards, at least. Now a new argument has erupted that has shades of the blue/white dress controversy.

Many people on social media sites are arguing whether the picture below shows a turquoise and grey shoe, or a pink and white one.

What colour is this pic.twitter.com/uGflVxsAEt — the shoe thing (@TFILDOLANS) October 11, 2017

It is a hotly contested debate with understandably strong views on both sides. But the truth is, those suggesting it is blue and grey are spreading fake news. An original, unmanipulated image makes clear the footwear is really pink and white.



THE REAL SHOE IS PINK & WHITE OKAY⁉️

The second pic was with flash & darkened, so it looks teal & gray. (depends on what lighting ur in) pic.twitter.com/FlbO3OEEuC — alisha🎃 (@dolansmalik) October 11, 2017

That does not explain, however, why some people have described beginning to see the edited, grey image as increasingly pink over time.

Bevil Conway, a neuroscientist at the National Eye Institute in the US, explained that it was because people’s brains were trying to separate what they identified as colour cast by the source of light from that reflected by the surface they were looking at.

“Basically, your visual system is constantly trying to colour-correct the images projected on the retina, to remove the colour contamination introduced by the spectral bias in the light source,” he said.

“The sky is blue, but everything you see under a blue sky isn’t blue. This is because your visual system is pretty darn good at figuring out what part of the light that you’re seeing is caused by the light source, and what part is caused by the surfaces themselves. We only really care about the surfaces – this is the part of the light that tells us about objects. The color of the light itself is usually pretty meaningless.”

Conway said the debate was similar to the famous one over the dress because they were both related to issues of colour constancy.

The manipulated photograph, he explained, had a lot of the turquoise cast over the whole image. “When you first look at it, after having looked at the pink version, your visual system is still adapted to the lighting conditions of the pink version and so you see the turquoise in the other version, and you attribute this to the shoe itself.

“But, after a while, your visual system adapts to the turquoise across the whole of that image and interprets it as part of the light source, eventually discounting it and restoring the shoe to the original pink version – or, at least, pinker.”

He said people could reset their visual systems, and see the shoe again as turquoise, by looking back at the original photo, or even just by looking around the room, as long as it was not illuminated with a turquoise light.

“Everyone has a very strong prior belief that shoelaces are white. So when your visual system sees the manipulated photograph, where the shoe laces are a weird turquoise, it then subtracts that colour from the rest of the scene, restoring the canvas of the shoe to pink,” he said.

“In the original photograph the human hand is clearly a normal colour, whereas in the other photograph it is clearly weird. So when your visual system sees the weirdly lit hand, it tells your brain ‘hang on, the colour of the light must be kinda funny, fix it!’”

