Popsugar Fashion Kate Middleton The Royal Dress Code Rules There Are Very Specific Rules When It Comes to Dressing For the Royal Calendar June 25, 2017 by Marcia Moody View On One Page Photo 17 of 22 ADVERTISEMENT () Start Slideshow Share This Link Copy ← Use Arrow Keys → 17 St. Patrick's Day — March Kate: Daytime formal with a hat. In a nod to the occasion, Kate usually wears green, but she did once wear brown. William: His colonel of the Irish Guards uniform. Previous Next Start Slideshow The RoyalsKate MiddletonThe British Royals