Mystery of colour-changing dress solved

The way you interpret the colour of a dress that confounded the world may depend on when you normally wake up.

The dress made by the label Roman Originals.

One cold winter’s afternoon in 2015, just as dusk was falling, Cecilia Bleasdale took a photograph of a black and blue dress she was thinking of wearing to a wedding. Then she posted it on social media.

What happened next was, said Pascal Wallisch, from New York University, “like a bomb” in the world of colour vision and so confusing that only now do experts have a theory about what was going on: the way you interpret the picture she posted depends, in part, on when you normally wake up. Some people saw it as white and gold, some looked at the same image and thought it was blue and black.

Researchers realised they had no explanation for why people saw the dress differently. So Professor Wallisch conducted a survey of 13,000 people to find what assumptions and conditions might cause one person to see it as gold and another as blue.

He found the ambiguity of the lighting on that late winter afternoon was crucial, leaving it poised between looking as if it was in shadow, in daylight or in artificial light. So too, though, was a more unexpected factor: whether you were a night owl or a lark. “If the brain faces uncertainty, in general it doesn’t say, ‘I don’t know’, it says, ‘I’ll fill in the uncertainty with assumptions’. The bottom line is, people made different assumptions,” he said.

Among those who thought it was backlit and in shadow, 80 per cent saw it as white and gold. “Why? Because shadows are blue, and so your brain subtracts blue light from the image.” That left it looking yellow.

The brain makes a similar adjustment to the bluish light of natural daylight, so people who assumed the photograph was taken outside were also more likely to see it as white and gold.

Why did some people think it was taken in artificial light, others that it was outside?

Professor Wallisch reported in the Journal of Vision that perhaps the critical factor was the light that people were used to — and that depended on their sleeping habits.

But Professor Wallisch and his team still cannot recreate the illusion in other images. Until then, the picture is a reminder of why we should be tolerant of all differences.

“If I tell you the dress is white and gold but you see blue and black, your view doesn’t change,” he said. “It just pisses you off. The same is true in politics. I need to start respecting that you might see world differently to me, and fundamentally believe it.”

The Times