A picture of a two-tone dress has gone viral after it prompted a fierce debate over whether it was white and gold - or blue and black.
Caitlin McNeil put the picture on the website Tumblr after she and her friends could not agree on the colour.
It was an image of a dress that a close friend’s mum was planning to wear to her daughter’s wedding.
The picture, posted on Thursday, went viral and sparked a fierce debate - using #The Dress - with even a few celebrities having their say.
You can vote on what colour you see here.
The debate is focused on whether the dress is white and gold striped or blue and black, with equal numbers appearing to see each.
Kim Kardashian tweeted: "What color is that dress? I see white & gold. Kanye sees black & blue, who is color blind?"
Taylor Swift said: "I don't understand this odd dress debate and I feel like it's a trick somehow. I'm confused and scared. PS it's OBVIOUSLY BLUE AND BLACK."
Actress Julianne Moore said: "What’s the matter with u guys, it’s white and gold."
The reason there is a difference of opinion can be explained by the way our brains process what we see.
"The phenomenon of colour constancy means your brain will adjust the colour of an object depending on its surroundings or illumination," said Ashley Wood, a lecturer and optometrist at Cardiff University.
"So if there’s a lot of blue in the environment, for example, the brain will subtract blue from the image your eye sees."
"There’s also the process of colour adaptation, where the colour you perceive is affected by what you have previously been looking at.
"This effect is easily demonstrated as an after image, if you view something that is red for 30 seconds, then look at a white background it will appear green for a short time.
"Depending on the context it’s probably one or both of these effects which are allowing people to see the image differently."
Ms McNeil, 21, from the island of Colonsay in the Hebrides, plays guitar and sings in a band called Canach.
She played at her friend’s wedding. When she got there she found out just what colour the dress really is.
The dress comes from the clothing website Roman Originals - and it really is blue and black.
