Flag of Scotland
At various times throughout history colours as light as sky blue or as dark as dark navy blue have been used (a selection apparently motivated by which colour of blue dye was available at the time). When incorporated as part of the Union Flag, the navy blue colour used was that of the Blue ensign belonging to the historic 'Blue Squadron' of the British Royal Navy. Dark blue was primarily used for reasons of expediency—it suffered less from the effects of fading resulting from prolonged exposure to the elements (namely sunlight and salt spray).