Apparently someone in the receiving line told Catherine she looked very lovely, and then said to William that despite Will not knowing who he was he wanted to assure him he wasn't hitting on Will's wife. Ha!
I am surprised by her choice of earrings on this night as she has the very substantial diamond drop earrings with emerald pendant, which were a wedding gift, and the emerald pendant part can be worn separately if she wanted a toned down look. Which she has worn before.