Believe it or not, there are still people who think it's perfectly acceptable to show up to someone else's wedding wearing white. Unless it blantantly says on the invitation that family and friends should rock white attire (after all, it does look crazy chic —Solange Knowles's wedding is proof!), by no means should a wedding guest wear the bridal color to another lady's big day.
What should I do if someone shows up to my reception wearing white?
Although the rule is considered to be "old school," it still rings true today. It's a major wedding faux pas. There are plenty of colors that a person can wear to a wedding, so you'd think they would leave white (and any other bridal-esque shade like ivory, bone, champagne and blush) to the bride — but that's not always the case. If someone shows up on your day wearing a hue that's eerily similar to your gown's color, unfortunately, there's not much you can do. Just try to the best of your ability to let it go and try not to show that it bothers you.
Also, you're probably not the only person who noticed. The guest who is wearing white is almost certainly garnering a lot of stares and whispers from your friends and family members. Hopefully, she will get the hint and not wear white to the next wedding she attends.