The whole idea of not wearing white comes from the fashion, started by Queen Victoria, of wearing a white gown to get married in. It showed that you could afford a new, impractical, dress to wear once. Usually women just wore their best dress, whatever colour that may have been.
But a lot of women couldnt afford an extravagant wedding dress so wore a more ordinary outfit in white. If another guest also wore white then there could easily be confusion. My grandmother married in 1939 and wore a white suit, my other grandmother married a few years later and wore a wartime version of the same outfit. So yes, then I could understand it.
But now with most brides wearing proper bridal gowns, it hardly like anyone will mistake the woman in an off the shoulder jumpsuit with a bride in full frock and veil! Seems a bit silly to get so upset over it to me. I mean lets face it, all of your guests have been invited by you or your (now) husband. Even if one of the guests hasnt met you, say his cousins plus one, the fact that you are in a wedding dress saying the vows, cutting the cake and standing in the middle of all the photos means that there really isnt much room for confusion!
Only exceptions I would understand would be low key or destination weddings and then it would be perfectly understandable for the bride to say "I will not be wearing tradition bridal attire so please avoid white/ivory/cream".