Between being a wedding planner for many years and having a large friend/family network, I've attended a lot of weddings. With each one, I've found there are two types of guests: the good and the who-invited-that-person. I wish I could stand at the entrance to each wedding and pass out a list of tips on how to be a good wedding guest.
It's the bride's privilege to ask her wedding party to dress a certain way for her wedding. It's tradition. She can tell them what jewelry and shoes to wear, too. She can even ask everybody to wear their hair up, or down, if she's super picky. But she absolutely, positively CANNOT ask anybody in her wedding party to alter their physical characteristics in any way.
A good positive attitude going into your wedding day makes all the difference, and so does a bad attitude. If you are going to have a negative outlook, it just breeds more drama into your day, creating more negative energy. I've seen this happen with brides a million times - creating drama that isn't necessary.