Clearly it really depends on the kind of wedding, and the kind of folks that will be there. The last three weddings I went to involved: the wedding party learning and leading a very earthy Brazilian dance to get down to, everyone including the wedding party disrobing and running into the surf naked on a secluded beach, bridesmaid's gowns cut low to showcase full back tattoos.... there were older relatives at these events too.
I think getting a sense of vibe and cultural traditions to be respectful makes perfect sense, but on the other hand, most couples want their friends and family to be comfortable at the wedding. Is someone at the wedding who is more fixated on jacket color than the fact that you came to help usher in the union really someone whose opinion you should give weight to?
The assumption that there will be professional photographs of the general crowd (rather than just the bridal party) and that someone might be noticeable in these casual unposed shots, is something that might apply to a small subset of weddings. Are guys supposed to avoid white shirts? I get that there are regional and probably economic differences at play here.