Ever wonder why your passport is blue when the person next to you at the airport has a red one?
Passport colors are derived from four primary colors: red, green, blue or black. Within these colors there are different hues and shades used to make the covers. Geography, politics and religion help determine what color your country’s passport will be. Rules dictate how passports must appear, including their size and format, which are issued by the International Civil Aviation Organization (ICAO) but governments around the world can choose the colour and design of their national document.
For example, passports for countries within the European Union (EU) tend to be burgundy, while those from Caricom (Caribbean Community and Common Market) use blue, which could be for geographical or political reasons.
For others, the chosen passport color may be religiously significant, such as in Muslim countries including Morocco, Pakistan and Saudi Arabia, where their passports are different shades of green. Some countries choose a certain color to reflect their unique identity, such as Switzerland, whose passport is bright red. Singapore’s has a bright orange/reddish cover.
A standard passport cover includes the name of the issuing country, a national symbol, a description (e.g., passport, diplomatic passport), and a biometric passport symbol. The choice of color, though influenced by culture and history, also comes down to practicality and availability. The card stock used to make the covers is supplied by a third party and only comes in certain color combinations. Countries like to add certain features to the covers to make them unique, like images, or hidden artwork that can be seen under UV light. This also helps in identifying forgeries.
(Information obtained from Wikipedia and Google search articles).