No one knows how to dress for a wedding better than those wedding-guest pros, the Middleton Sisters. The most recent example was just on Sunday, when they watched family friend Thierry Kelaart walk down the aisle. (The bride was accompanied by their father, Michael Middleton!) Their choices reflected the still-warm weather: Kate wore a floral-covered periwinkle Erdem dress and Pippa sported a laser-cut coffee-hued dress with a matching jacket on top. See more of the royal's best outfits by clicking through the gallery.