Melania asked the pope to bless a gold rosary and he did and Ivanka wore

[Staph]

5. Though the rules have relaxed somewhat,

the traditional attire for a woman in a private audience with the Pope would be a black dress or skirted suit, below knee length, covering the shoulders and with sleeves. Some sort of hat or mantilla was also expected. Limited jewelry. Light or no perfume/cologne.

Though if you were a Catholic queen, you could wear white instead -- privilège du blanc.

Wikipedia is my friend. Check out Audience (meeting).

I actually like what Melania was wearing. It was much better than the black jumpsuit with the WWE belt that she wore in Saudi Arabia. She rarely wears her hair up, so that was a nice change of pace.