Buffy: Willow, you’re a gay woman! And he... isn’t.
Willow: This isn’t about his physical presence! It’s about his heart.
Anya: His physical presence has a penis!
This outfit makes a quick appearance in the season 7 episode "Him". The top is a silk lace top by Nanette Lepore. The blouse appears purple, but it is actually blue. I know this, because I own the original screen worn top.
During the later seasons, cast members a lot of times would pick their own outfits. I wouldn't be surprised if Sarah Michelle Gellar picked this top, because seems to be quite the fan of the designer.