Y'all make me really glad that in my days as a Christian minister, I was protestant. (Pentecostal if you want to get picky and specific about it.) I didn't have a dress code. Of course, now as a pagan, for me the thing to wear to perform a wedding would be a ritual robe. Or nothing, as some pagan handfastings are performed skyclad. But I think if it's a ceremony with spectators, a robe is the way to go. Color choice up to the bride, of course.