What color corsage would match a prominently black dress with a white top?

Black and white are neutral colours. You get to pick any colour for the corsage and it will all look good. My suggestion is to pick the lady's favourite colour, or a colour that is important to her.

Otherwise, red will look dramatic, pink will be sweet or innocent depending on your interpretation, a deep yellow is quite striking and orange is very "hot", blues of any shade are cool and sophisticated while purple is regal.