This is what I wore at the reception of my cousin's wedding. I love the red dress I wore as her maid of honor but I know that I must be in comfort yet stylish still so I changed into this outfit.
I have a standard of what to wear at weddings, except when the theme asks for but if there's none, then for me I think it is best to be in pastels or light-colored clothes so you will not clash with the wedding atmosphere or be an attention-grabber which the bride should only be. Which lead to another rule of the thumb that is never to be broken- NEVER, EVER wear an all white or black outfit to a wedding because these color is attached to mourning. Wearing white also disrespects the bride in my own opinion. But of course this rule is unnecessary if the wedding theme says that invited are supposed to wear white or black.
Prints should also be observed in choosing your ensemble at weddings. It should not be too bold and distracting. Plains are better but prints like floral are very much accepted.
Just always follow the rules at wedding invitations about what you will wear and you'll never be underdressed or overdresssed