This. As in the AWI, regiments could have a different coat colour each year (if they got a uniform at all, in that particular year). And the King's Lifeguard is pretty much the only unit I can think of, pre-NMA, that had coats and flags the same colour - certainly the "coloured" regiments of the London Trained Bands were based on their flags, not any uniform clothing.
Also, very few flag manufacturers make more than two flags for each regiment, so this way you've managed to make yourself four with a common design.
