Historically, Colour Sergeants of British line regiments were tasked with protecting Ensigns, the most junior officers who were responsible for carrying their battalions' Colours (flag or insignia) to rally troops in battles. For this reason the Colour Sergeant rank was considered a prestigious one given normally to courageous Sergeants who had attained accomplishments in battles. This tradition continues today as Colour Sergeants form part of a Colour Party in military parades.
Colour Sergeants are referred to and addressed as "Colour Sergeant" or "Colour" ("Colour Sergeant Bloggs" or "Colour Bloggs", for instance), never as "Sergeant". Unusually, NCOs with the rank of Colour Sergeant who hold the appointment of Company Quartermaster Sergeant are still addressed and referred to by their rank, not their appointment.
Canadian usage
Colour Sergeant is also a rank in the foot guardsregiments of the Canadian Forces, specifically the Governor General's Foot Guards and the Canadian Grenadier Guards. It is the equivalent to Warrant Officer; a Colour Sergeant wears the rank insignia of a Warrant Officer (a royal crown) on all uniforms except No. 1 Ceremonial Dress, on which a special rank badge is worn: three chevrons, point down, surmounted by an image of regimental colours.
They are addressed as their British counterparts are.