But Vogue's queen bee makes her own fashion rules. On Wednesday evening, she waltzed into the White House for the formal State Dinner wearing a white Chanel Spring 2009 couture gown -- the same one she wore to the 2009 Costume Institute Gala at the Met.
Anna swept past reporters last night (stopping only to mention that her dress was by Chanel, natch) then joined guests including George Clooney, Harvey Weinstein, Marchesa designer Georgina Chapman and of course President and Michelle Obama and Prime Minister and Samantha Cameron in the tents on the White House South Lawn.
Wintour made for an ideal guest at the event, which honored British Prime Minister Cameron and the UK's chummy relationship with the United States. Anna was just one of several British celebs in attendance, including several "Downton Abbey" cast members.
She also, of course, is a key Obama supporter, having raised at least half a million dollars for the president's reelection campaign. We're not sure whether that includes money raised from her fashionable Runway To Win project, but it certainly includes the cash brought in from not one but two fancy New York dinner parties she's hosted in Obama's honor over the past two years.
Which is all to say that she can wear anything she pleases to the White House. They'll just be glad she came.
See Anna in her Chanel Couture last night as well as at the 2009 Met Gala. Are you a fan of the dress?