14. Women should not wear colored nail polish.

Reason: It appears to be a royal family decision.
Exception: It’s not enforced too strictly.
This one is a little contentious because some people insist it’s true, while others claim it’s not. It’s safe to say that the Royal Family has very specific fashion guidelines, and many of the women in the family have opted to dress neutrally for many formal events.

Colored nail polish is a big no-no for women. ©Max Mumby/Getty Images/Indigo
However, Princess Kate has occasionally sported red fingernails, suggesting that this rule—which some claim the late Queen instituted—isn’t always strictly enforced. Rather than being a strict rule, this is probably best described as a royal preference.