Errol Laborde, writer of Marched the Day God: A Record with the Rex Group, offered a principle that the colours ended up depending on heraldry: all 3 colors correspond to a heraldic tincture, and Rex's goal could are to produce a tricolor to signify their "kingdom". Purple was broadly connected https://elliotbecuo.bloggazzo.com/3084968/the-2-minute-rule-for-mardi-gras-world-of-new-orleans