Passports around the world are only made in four colours: black, blue, red and green.

There are no official rules or regulations governing what colours passports can be. Countries are free to choose whichever colour they want.

The reason why passports are black, blue, red or green, is simply because these colours look the most official. Dark colours also hide signs of dirt and wear and tear.

South African travel site Traveller24 reports that the choice of a passport colour can be determined by culture or historical significance. Green is mostly used in Islamic countries as it carries religious significance, while red is preferred for countries in the EU. South African passports are commonly known as the “Green Mamba,” but why green was chosen remains a mystery.

1867 different colours from which to select

William Waldron, the vice president of security products at Holliston, LLC (which makes passports for more than 60 countries) told Travel & Leisure that they can manufacture “any colour that’s in the Pantone book.” That is about 1867 different colours.

There are, however, certain rules that all countries must follow.

Passports should be made of a material that can bend, doesn’t crease and can resist chemicals, extreme temperatures, humidity and light.

The International Civil Aviation Organization (ICAO) also makes recommendations about typeface, type size, and font.

Click here for more information.