Duchess Kate Middleton will never wear nail polish in public -- here's why

Being a royal means hundreds of engagements -- public benefits, black-tie galas, weddings for your very distant cousins you've met once. Many of us assume that dressing in high heels, a gown, Princess Diana's tiara and a much-coveted blue sapphire engagement ring warrant a fresh coat of polish, but that's not always the case.

Interestingly enough, Duchess Kate -- or the queen, for that matter -- isn't allowed to wear nail polish, unless it's a natural or clear color for an official royal event. The firmly-held royal rule applies for gels or acrylics or anything fake.

It seems even Megan Markle is opting for the less-is-more trend, instead sporting neutral nails while out with Prince Harry.

But if the queen were to wear one color, it would be this classic $9 go-to by Essie. The Duchess even opted for a similar custom shade for her wedding day.

Related: Behind-the-scenes of the royal wedding