I don't think you should be wearing a white dress to a wedding. out of respect, it's usually preferable for guests to wear anything other than white just in case people mistake u as the bride.
wedding 101 on what to wear to a wedding:
http://www.weddingchannel.com/ui/buildArticle.action;jsessionid=aHcH02R6gw3e?assetPath=%2Ftemplates%2FArticles%2FNonContentSet%2FGuests%2Farticle_1152.html 
So what colour are u suggesting huh? White is the universal colour for weddings. Are u suggesting girls should wear colours like brown or black to weddings? That is even more absurd. You are just saying this becoz the bride isn't as pretty as Xiaxue and u thought she was the bride am i correct? Remember this, brides do not necessarily be the prettiest girl around. If not only the prettiest girls get to marry. Universal wedding colours are supposed to be light colors like white, pink, yellow and blue. All in light tones. There are no rules stating that white is for the bride. Neither is black only for the bridegroom. Think about it, what are guys suppose to wear if only the bridgesgroom is allowed to wear black? U would come out with a pink tuxedo maybe? =)