If I'm wearing a strapless ivory gown can the groom wear a back tux with a white shirt, black vest? We were told he has to match my dress - how so? Would we clash in our pictures?
Yes, he can wear a back tux with a white shirt and black vest. I don't know what that person was referring to unless it is about formality. He really shouldn't wear a tux if the wedding is during the day. And yes, you should be conscience of colors being similar because of the visual appearance and pictures. But, your clothes seems appropriate.
Maybe I am missing something that someone else won't.