My fiance and I are planning a rustic/earthy wedding in Brooklyn next summer. I really would like to eliminate black (and gray) attire from our wedding party and photos. The problem is that it's an evening wedding and our families will want to make it a bit more formal. If we put the groomsmen in tan suits, can we still put "black tie" or "black tie optional" on our invitations? In other words, is it acceptable for the groomsmen to be "less formal" than maybe some of the guests. The wedding as a whole will be formal, I just want to keep the wedding party in earthy tones. HELP!