Not all of the seven Emirates that build up the UAE have the same flag today, but that wasn’t always the case – red has historically been used for all of the emirates’ flags to mark ports, making it easy for ships to locate harbours. There is also rumour that in earlier times (around the turn of the century) the flag of Abu Dhabi was plain green, as used in many Islamic countries. But that lasted for no more than 10 years or so before being changed to red.
In 1958 Abu Dhabi adapted the plain red flag, adding a white vertical stripe. Later this was reduced to a canton (a rectangle) in the top left corner.
In 1971, of course, the UAE flag we know today was adopted. This features the so-called pan-Arab colours – red, black, white, and green – to symbolise Arab unity. Each of the four colours is supposed to represent a particular Arab dynasty or caliphate – white for the Umayyad, the second caliphate (7th-8th centuries, centred on Damascus); black was the colour of the flag of the Abbasids (8th-13th centuries, centred on Baghdad); green for the Fatimids (10th-11th centuries, based on Cairo); and red for the Kharijites (late 7th century AD, concentrated in what is today southern Iraq).

 

[Originally published in Abu Dhabi Week vol 2 issue 22]