Open Back Blue Floral Print Long White Lace Prom Dress PromGirl The Story Behind Keira Knightley's Emerald Green Slip Dress From 'Atonement' Vogue Anyone else still thinking about Keira Knightley's backless green dress from Atonement, 13 years later? At the link in bio, our style editor examines why the backless trend became an unlikely Backless Dress Keira Knightley Atonement Dress Atonement Cecilia Green Long Dress Backless Maxi Dress Keira