Royalty & Legacy: Balls - Gala outfit

My Sim held a grand ball and selected "Gala" as the outfit theme. Sims arrived in the classic crazy NPC mix of random wear, but most of the clothing from Royalty & Legacy. I'm not certain what "Gala" means for Sims but typically in RL it is a black-tie affair so it seems Sims would wear their formal wear. Has anyone managed to alter/control those outfits for the non-playable Sims? A Google search showed other players asking about this but the only answer has been to shift-click and change the Sims' outfits to one of their other categories, which isn't what I want.  Any insights, like, am I expecting too much (again)? :D