The origin of royal blue color

Sky blue originated from a dark blue stone, which is now called celestite. This color was first used in the old French territory in the12nd century, and was first recognized by Louis IX (St. Louis) as the color used by the royal family. Since then, it has been widely used and circulated by the French royal family. In heraldry, royal blue is called blue, and there is no other blue in heraldry. Since the French conquest of Britain in 1066, royal blue in English has been brought into English from French or German and has become a specific vocabulary.