Look back at the rainbow-hued wardrobe of Britain's longest-reigning monarchFrom left: Queen Elizabeth arrives at the Guards Polo Club at Smith's Lawn in Windsor, England, for a polo match on June 20, 1973; Queen Elizabeth inspects members of the armed forces as she attends the Ceremony of the Keys with Prince William (not pictured) at the Palace of Holyroodhouse in Edinburgh, Scotland, on June 28, 2021; Queen Elizabeth visits a new maternity wa…