Reading through this thread, with reactions from what I would assume is a reasonably broad cross-section of society, my conclusion is that if a bride decides to make this nitpicky type of request, while some guests will be OK with it, quite a few will not. Is it really worth being remembered by family and friends as “you know, the Bridezilla who made me buy a differently-colored dress” in order to get what you think are slightly more aesthetically pleasing photos on
Instagram, or to avoid the utterly horrifying situation of someone momentarily thinking that a guest who is not part of the bridal party is actually part of the bridal party? Be that Bridezilla if you want, but just bear in mind that lots of people will resent it and will be talking about you for years afterward.