Bridesmaids are wearing chocolate brown, groomsmen are wearing black and brown. MOB is wearing black slacks. I have a beige evening dress. As the MOG is this an appropriate color? Since the MOB is wearing pants do I need to dress down. The wedding is in the evening.
Your dress is fine in color, because it blends with the black and the brown. But it may be more formal than the MOB. So, you may have to dress down. I don't know how formal her slacks are or how formal her outfit may appear. Only you will be able to make this decision. Just be sure you aren't 'outshining' her.