Approaching immigration control, have you ever wondered why your passport, and the passports of those around you, are the colours that they are?
OK, perhaps not - the airport experience is enough to frazzle our sense of curiosity. Nevertheless, there is much more to it than you might think.
According to Hrant Boghossian, the vice president of Arton Group, which runs the interactive passport database Passport Index, the shade of each national passport is derived from just four main colours: red, green, blue or black.
However, "within each colour hue, we see vast variations," he told Business Insider. "There are in fact many passport colours."
While rules that dictate how passports must appear, including their size and format, are issued by the International Civil Aviation Organization (ICAO), governments around the world can choose the colour and design of their national document and there are "many possible scenarios" that explain why they choose to go with a certain colour, Mr Boghossian said.
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The passport books for countries within the European Union (EU) tend to be burgundy, while those from Caricom (Caribbean Community and Common Market) states use blue, which could be for geographical or political reasons.
"Some could argue that the burgundy red is due to a past communist history," said Mr Boghossian, and that blue passports may be symbolic of the New World for countries in North America, South America and Oceania.
"The passport of Turkey has changed to burgundy as it hopes to join the EU," he also claimed.
For others, the chosen passport colour may be religiously significant, such as in Muslim countries including Morocco, Pakistan and Saudi Arabia, where their passports are different shades of green.
"Most Islamic states use green passports because of the importance of the colour in their religion," Boghossian said.
Green is believed to have been a favourite colour of the Prophet Muhammad, is "symbol of nature and life", and is seen on several of the national flags of Islamic countries such as Afghanistan and Iran.
Some countries choose a certain colour to distinguish itself and reflect their unique identity, such as Switzerland, whose passport is bright red. Singapore's bears a bright orange/reddish cover, while Canada's temporary passport book for travellers in need of emergency travel documents has a white cover.
The US jacket has seen several changes in colour, from red and green and now blue.
The choice of colour for a country's passport, though potentially influenced by culture and history, also comes down to practicality and availability.
"Passport production is a highly controlled process, and only few companies around the world are doing it," Mr Boghossian said.
The cardstock used for passport covers is "usually supplied by a third party" and "only comes in certain colour variations to meet the required standards," he added.
While the colour of passport books may be limited to shades of red, green, blue and black, its design is said to be "entering an exciting age" with several countries incorporating special features into their passports.
Several, including those used by citizens of Canada, Britain, the US, China and Norway, feature 'hidden' artwork on their pages that appear under UV light.
Norway's sleek new passports, designed by Neue Design Studio, are offered in either white, turquoise or red and its pages feature minimalist interpretations of the country's most striking landscapes and scenery, including the otherwise elusive Northern Lights phenomenon which appears when placed under UV light.
In 2012, Finland introduced a feature in its passport, where images in the bottom of its pages turn into a running moose when travellers flip through their passport.
A few Britons are believed to hold a unique Queen's Messenger passport in Britain, which are said to be issued only to individuals relaying important messages or information to British consulates and embassies around the world.
See an interactive graphic of different passports around the world at the Passport Index website here.
The Telegraph, London
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