I just went for a walk and saw a bride and groom get out of a car and walk into the Brooklyn Municipal Building to get married. How did I know they were getting hitched? She was in a mini-white dress, he in a suit and she was carrying flowers.
In addition to her white dress and shoes she also had on white underwear. How do I know? Because her dress was so sheer that I could see them. She needed to wear a slip and I can't believe that no one who saw her in the dress at the store or at home told her that.
Please do yourself a favor and make sure that your undergarments are not seen at all either by wearing a slip or having a lining sewn into the dress. You can easily have your seamstress sew cups into the bodice so you don't need a bra but panties are a separate item that you will need to buy and ask someone if they can see them through the skirt fabric.
I was too far away to get a picture to run with this post, but take my word for it - she had on white briefs and all of Downtown Brooklyn saw them.