We've all stood in long queues, dealt with unscrupulous 'touts' just to get that coveted blue booklet; but do we actually know why Indian passports are blue in colour? Or for that matter, how is the colour of a country's passport decided?

Countries have the liberty to choose the colours of their passports, something which, the "broad spectrum" of passport designs lays testimony to.

However, there is a general trend that is observed when it comes to countries and passport colours.

Source: Reddit

Usually Communist nations or nations that were formerly under the Communist regime, have red coloured passports. 

Source: Financers

Islamic nations have passports that are green in colour.

Source: Twitter

Regular EU passports are burgundy red.

Source: Mopo

And then there's this awesome looking Swiss passport, that stands out!

Source: Le News

The rest of the nations mostly use shades of blue for their passports. 

Source: Taringa

Several countries have adopted common designs through mutual consent.

The members of the CA-4 Treaty (El Salvador, Honduras, Guatemala and Nicaragua) have a common design passport, known as the Central American passport, which is navy blue in colour. 

Source: Wikimedia

The Andean Community of Nations: Ecuador, Bolivia, Colombia and Peru began issuing common designed passports in burgundy-red. 

Source: Passports

The members of the Caribbean Community (CARICOM) recently started issuing passports bearing a common design (CC), that are dark blue in colour.  

Source: Wikipedia

In addition, one nation may offer differently coloured passports to officials & diplomats. This is to help identify the bearer.

Usually the three different categories of passports in India are: Diplomatic Passport - maroon, Official Passport - white, Regular Passport - blue.

Source: e-Governance