I think the request is odd, but nevertheless, I think the polite options are to decline or accept the invitation that was offered, including wearing black.
For a wedding it seems unusual, but a white ball or a costume ball or a masquerade ball are not unheard of and it would be quite rude to show up to any of those without abiding by the dress code. I can't think of a way that showing up to this and ignoring the dress code would be the right thing to do.
But a wedding isn't any of these things. It just isn't. It's pretentious, shallow, faux-celebrity-ish and rude, rude, rude to micromanage what your guests wear to your wedding. (Level of formality, ok. If your reception is being held in a venue that doesn't allow jeans, then it's ok to require your guests to not wear them. It's never
ok, at least in U.S. weddings, to expect male guests to rent clothes or any guest to wear a specific color).
And I think you'll find that even for a black and white ball that there isn't, as far as I know, a way within etiquette to refuse entrance to an invited guest who doesn't abide by the dress code (although in that case the guest is the one being rude). Or if there is, I'm not aware of it.
And now you have me thinking of Bette Davis in Jezebel
(who, at a ball where all the women are expected to wear white, wears flaming red. It doesn't end well for her.)