It's traditionally seen as a major wedding no-no.

But Duchess Kate threw caution to the wind for the Royal Wedding... seemingly wearing an all-white outfit. Awks. https://twitter.com/mcnulty_joshua/status/997794632057712641 The mother-of-three - she only gave birth to Prince Louis a few weeks ago - arrived at Windsor with her elder children Prince George, aged four, and Princess Charlotte, three. Both children are part of the wedding party for Meghan and Harry's Big Day. https://twitter.com/ABC/status/997795498307280896 We've looked at the footage and there is no doubt that her dress, jacket, and hat appear absolutely white. Apparently, however, it is in fact YELLOW - with the sunshine giving it its distinctly white hue. https://twitter.com/RE_DailyMail/status/997794281934016512 According to Rebecca English, the Daily Mail's royal correspondent, the Duchess of Cambridge "wore a primrose yellow wool silk tailored coat by Alexander McQueen. "The Duchess of Cambridge is wearing a hat designed by Philip Treacy and shoes by Jimmy Choo." https://twitter.com/msmerrythought/status/997797208274677766 We're still waiting for a decent, proper look at the outfit before making a final call on whether her attire is indeed white... or more of a pale yellow.