I'm not bothered that I haven't been invited to the whole thing, tbh I didn't expect to be invited at all. There are lots of people I know going and it will be a fun party.
However, I'm really not going to spend the whole wedding guest thing on something I won't wear again and in any case, do you dress for a wedding or for a party when just going to the evening do? Do usual rules about black/red/white apply?