At the last count, 42.5million of the UK's population of 64.1 million hold a passport.
Whether foreign or British, these passports will adhere to one of just four colours.
You've probably noticed how passports don't come in a rainbow of different hues and shades. They tend to be quite unadventurous in colour.
As for the small selection, there's a reason for each one.
Here's what each colour is - and what each one means.
As any Brit knows, when it comes to UK passports, deep red is the colour of choice.
It also happens to be the most common passport colour with all members of the European Union, apart from Croatia, sporting a burgundy hue.
BATH, ENGLAND - OCTOBER 10: In this photo illustration, UK passports are seen on October 10, 2016 in Bath, England. Since the UK voted to leave the European Union in June, the UK's currency has been fluctuating in value against other currencies, including the Euro and the dollar, and looks likely to remain doing so while the uncertainty remains surrounding the terms of the UK's departure from the EU. (Photo by Matt Cardy/Getty Images)
The Economist called this a "branding exercise" - though there's no word on whether we'll stay a nice shade of EU red once we've left it.
It's not just EU states either. The Andean Community (also known for past EU-ambitions) of Bolivia, Colombia, Ecuador, and Peru also has burgundy passports.
Switzerland matches its passport colour to its bright, red flag.
In second place is the colour blue, reports Travel and Leisure.
Blue reportedly symbolises "the new world" with 15 of the Caribbean countries opting for it.
Further south down the South American continent, Brazil, Argentina and Paraguay also use a blue passport – the cover symbolising the connection with the Mercosur trade union.
The United States are said to be changing their passport colour again in the near future
Venezuela, on the other hand, still uses a red passport, a throwback from its time in the Andean Community.
The most famous blue passport in the world though has to be the one issued to US citizens – but this was changed to blue as recently in 1976.
Owing to the importance of the colour green in Islam, most Islamic states reflect this in the colour of their passports.
Mexico's is also green
Examples are Morocco, Saudi Arabia, and Pakistan.
Variations of green are also used by members of ECOWAS - Economic Community of West African StateS - including Niger and Senegal.
The reason for the least common passport colour may be rooted in practicality - as may all of them in fact.
Thailand also issue a black passport to their citizens
The dark colours chosen obviously don't show up dirt as much, and they look nicely official.
The Republic of Botswana, Zambia and New Zealand issue band passports, though it should be noted black is New Zealand's national colour.