I'm not a massive fan of waistcoats worn as stand alone pieces. How formal is the dinner? Do you have to stick to suiting or can you be a bit more creative?
If the case is the former, lose the waistcoat and stick to a two piece. Black will work but I'm not a massive fan of black and pink. A dark navy would work better.
If the case is the latter, how about losing the tie? Undo a couple of buttons, swap the waistcoat for a sports jacket and the trousers for chinos.
Need to know more about the cirmcustances before I can give proper advice mate.