By InStyle Staff
Updated Mar 29, 2012 @ 1:45 pm
Michelle Obama, Rachel Roy
Credit: AP Photo/Silvia Izquierdo; BEI Images

Designer and InStyle contributor Rachel Roy stopped by the opening of Valentino's Rodeo Drive store in her own design—a watercolor silk one-shoulder dress just seen on Michelle Obama! "I’m a big believer in one shoulder for cocktail," Roy told "It's one of my favorite styles." The First Lady agrees! "She looked amazing. I love when someone wears a nude tone, it elongates," the designer said of Obama's appearance in the dress at the Palacio do Planalto in Brazil earlier this month. Roy then added, "Her arms were beautiful." Click through the gallery to see our favorite looks from Rachel Roy's latest collection!

— Lindzi Scharf