Optical illusion: Dress colour debate goes global
A debate between family and friends about the colour of a dress for a wedding has become an internet sensation.
Alana MacInnes, of Uist, and Caitlin McNeill, from Colonsay, sought views on Tumblr about whether it was gold and white or blue.
The debate was picked up by fashion bloggers, Buzzfeed, the Washington Post and US magazine Wired.
On Twitter the debate's hash tag #TheDress was the top trending tag.
Other tags included #TheDressIsWhiteAndGold and #TheDressBlueAndBlack and the much less popular #TheDressIsBlue.
Wired has even looked at the science behind why people are seeing the dress as gold and white, blue and white, blue and blue or blue and black.
Professors have also joined the scientific discussion on Twitter, while celebrities including US singer Taylor Swift, talk show host Ellen DeGeneres, actor Will Smith's son Jaden and reality TV star Kim Kardashian have been tweeting about the debate.
Kardashian said she saw white and gold - but her husband Kanye West saw blue and black.
Why are people seeing different colours?
One possible explanation may be down to an optical illusion, stemming from how the human brain processes colours.
The brain's perception can be thrown by the colours of nearby objects, and their reflected light falling on the object in focus - in this case the dress.
Prof Stephen Westland, chair of colour science and technology at the University of Leeds, said the way people see colours varies hugely.
He said: "One in 12 men is colour blind. But what people don't know is that even if the rest of us are not colour blind we don't always see colour in the same way.
"The surprising thing is that this doesn't happen more often. People think if they take a photo of something, people will see the same thing but of course that is not true."
Prof Westland said that the "strange" lighting in the picture had probably contributed to the confusion.
He said: "If it hadn't been taken under very strange lighting this probably wouldn't have happened because if you look at the manufacturer's picture, it is indisputably blue and black."
Prof Westland explained that the confusion could stem from how we name colours, as there are often blurred lines between how we interpret what colour something is.
But he said this is an extreme case as "there is a huge difference between black and gold, blue and white".
He said: "It is possible that people could literally be seeing different colours but it's impossible to know what is in someone's head."
Buzzfeed's online story about the dress has been shared more than 20 million times.
Its post about the story also set a record for the website when 670,000 people went on to the site at the same time.
Dr Paul Coxon, a physicist at Cambridge University, has tweeted that if the dress was combined with social media users' love of cats "the universe would explode".
The picture of the dress was taken by Ms MacInnes and posted on social media by Ms McNeill.
Ms McNeill asked her followers: "Guys please help me - is this dress white and gold, or blue and black? Me and my friends can't agree and we are freaking... out."
The women are members of the Gaelic band Canach.
She said: "Two of my very good friends were getting married and they asked me to put together a band to come and play at the wedding.
"This was a wedding on the tiny island that we come from on the west coast of Scotland called Colonsay and about 100 people were there.
"A week beforehand the bride had been sent by her mother a picture of the dress she was going to wear and when the bride showed her fiance, they disagreed about what colour it was.
"She was like, 'It's white and gold' and he said, 'It's blue and black'.
"So they posted it on Facebook to try and see what their friends were saying but that caused carnage on Facebook."
She said they had forgotten about the dress until the mother of the bride wore it at the wedding, when it was "obviously blue and black".
Ms McNeill described the numbers of retweets, messages on Tumblr and celebrity interest in the debate as "unbelievable".
A spokesman for Roman Originals, which is based in Erdington, Birmingham, said the dress was also available in three other colours, including a red and black version.
He added: "It's black and blue but we're definitely looking into a white and gold version."