Yes, royals can wear lipstick. There are no official rules prohibiting them from doing so.
In fact, many royal women throughout history have been known for their signature lipstick shades. For example, Queen Elizabeth I of England was known for her love of red lipstick, which she used to create a dramatic and powerful look.
In modern times, royal women like Princess Diana and Kate Middleton have also been seen sporting various shades of lipstick, from subtle nudes to bolder reds. Their choices often reflect current fashion trends and personal preferences.
While there may be some stylistic guidelines or traditions within royal circles, the decision to wear lipstick ultimately comes down to individual taste and the occasion.