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Each regiment in the British Army has a flag, called its 'colour'. This dates back to at least the 16th century. In this citation from Certain discourses concerning the formes and effects of divers sorts of weapons, and other verie important matters militarie, 1590, Sir John Smythe appears to be disparaging about what must then have been new practice of calling an ensign (flag) a colour:
"Colours is by them so fondlie & ignorantly given, as if they should (in stead of Ensignes) be asked how manie Colours of footmen there were in the Armie."
The word 'colour' in this context is now best remembered via the annual ceremony in London of 'Trooping the Colour', in which various regiments of the British Army, notably the Household Division, parade their regimental colours before the monarch.