I think at a certain point it just gets pathetic.
I saw a post on Instagram once of a bride shaming one of her guests for turning up in a floral summer dress (blatantly not a wedding dress and looked very nice but not remotely upstaging the bride or trying to look bridal). My immediate thought was, "You just got married to supposedly the love of your life, and this, this is what you're choosing to focus on?"
Like if your wedding was shit, just say that because if a dress that your guest turned up in (that again was nice, not remotely upstaging, not bridal or revealing) is getting you so riled up, your wedding must have been dull as dishwater.
In the end, I thought the only rules were that you dressed smart and didn't wear a wedding dress or anything in white/cream/ivory (or whatever colour the bride is wearing).
I've worn a black cocktail dress to a wedding before. It had lace on, too, but it was in no way a dress that would have been suitable for a funeral, and given the fact that men freely wear black suits to weddings, the alleged faux pas because of the "funeral connotations" doesn't wash. If it's an unsuitable colour for women, then it's unsuitable for men, too.
Unless you're part of the family/bridal party-you're probably not going to even feature in that many of the pictures anyway. So, why does it matter if Patricia turned up in a pastel pink dress?
I do think some people need reminding about what the day is supposed to be about.