She has a black prom dress she told me. I have a black tux and a purple shirt and purple tie. Should I match her black dress? If so what should I wear? No bowtie suggestions please!

Black matches anything. If she would like to match tell her we will match. Purple and Black is not so bad.

I would maybe get a black tie but other than that you do match her dress.

back when i went to prom i had my tie and vest matching her dress.. though in your case since her dress is black, you're prob fine with what you have or just get a black tie/vest.