Well, last year alone I went to about 50 weddings.. Oh, I was photographing them.. I had one that was Greek Orthodox however other then a really pretty church nothing stood out more then another wedding. I don't recall the women having a head covering, but things like that can vary so I would ask someone who attends about that churches traditions where that is concerned. Now that being said at a wedding it's understood that there are going to be people of other faiths then the couples so I really wouldn't worry about it too much as "outsiders" will be accepted, I've had a few weddings that the priest/ pastor/ rabbi ect has even acknowledged that in the homilies/ sermon / blessings.. Ect. Obviously NO WHITE, I would think that would go without saying but you'd be surprised. A dress, top with skirt or even suit are all
Acceptable just as long as it's dressy and not casual. For church I would suggest a modest heel if you're going to wear them, and bring a second pair of shoes for the reception. Some girls eventually will even go bare foot, but to me that's nuts. At a "good" wedding, drinks will be spilled, glasses broken and the last thing you want is a bleeding foot! Just remember, if you plan on dancing then wear something that you can dance in. Hope that helps! I can't wait till wedding season again myself, the next one I photograph is Feb 16th so just around the corner!