Black Tie Wedding Guest dress by n a Pickle Wedding Guest Dresses Elegant Black Tie, Formal, and Cocktail Styles Which dress for a "Formal" attire wedding. Been to many black tie optional weddings but never "formal". Wedding is tomorrow in the Midwest. : r Weddingattireapproval Your dress code: Garden Party Formal. Your guests: Absolutely serving. I love a classic black tie wedding but something about garden party just speaks to me!!