Born and raised in Michigan, actually. I don’t think this is a southern notion, but it may be either fairly strict or old-fashioned. I’ve had discussions of these sorts of things with friends, though, and I think it’s a reasonably well-known rule among people I know. And they’re not necessarily originally midwestern, either.
Interesting comments regarding Jewish weddings, though. Of course, observant Jewish weddings are quite different in a lot of ways than the Christian (and Christian-influenced but not particularly religious) occasions I’ve usually witnessed. I wouldn’t be particularly surprised if the traditions are different regarding acceptable clothes for the wedding. I mean, if grandma and grampa can’t even stand next to each other during the traditional chicken dance . . .
People justify not believing in good manners in all sorts of ways - it’s dishonest, I’m not hurting anyone, it’s called self-expression, it’s shallow to judge people based on how the dressed, and so on. It’s also shallow to put your personal desire to wear black or red to a wedding ahead of the comfort and happy feelings of others. Like I said, if it was a non-mainstream wedding, with attendees and participants dressed in nontraditional ways, no problem. But if it’s in a church, and the bride’s wearing white, then even if they wouldn’t care (or, at least, wouldn’t care enough to make an issue with you) there’s still the bride and groom’s parents, and old Aunt Gertrude, and various other folks around. It’s a special day for Aunt Gertrude too, you know, and she may be more traditional than the newlyweds. And the newlyweds might not want to end up hearing clicking tongues later on, and they might not want to make excuses to Aunt Gertrude for what she perceives as boorish behavior.
After all, everyone knows a wedding’s only sorta about the people getting married. It’s also a family and community event, and etiquette is a set of principles for people to get along. And it’s especially good when people don’t know each other very well (not to imply that you can treat your friends rudely, of course.) Besides, most of us want others to like us, shallow as it is, and so we might make the deep, dishonest, shameful sacrifice of not wearing that black sweater if it makes others more inclined to think we’re decent folks.
But in the end, if you, like many other people, want to satisfy your own minor personal desires no matter what others may think, go for it. Aunt Gertrude’s tongue-clicking is probably a pretty reasonable response to that.