Some might have thought that the dress robes that Bellatrix was wearing where fitting for a Deathday party, but in reality she never wore anything that wasn't black. These however where dressy and therefore had a bit of green and silver accenting the dark material. She was making the rounds, doing what a pureblooded socialite did best...mingle. Though her eyes kept watching the new faces studying them and watching.
Her attitude seemed quite aloof for the night but that could have been because she was trying to listen to everything around her. Pick up on hints about the future anything that she could of course tell the Dark Lord later.