The emerald green silk gown worn by Keira Knightley in Atonement is a truly iconic costume, worn with delicate confidence by Knightley. The dress, a beautifully dyed deep green, made from the hues of three gowns: a lime-green silk, a black and green organza, and a green chiffon, hangs loosely off Keira’s smooth skin, her lithe frame seems barely able to hold the fragile straps on her slight shoulders. Knightley wears nothing but the airy gown and gold heels, her wrist and finger-waved hair simply adorned by a white-gold Chanel bracelet and a white-gold Chanel star hair-stud. The scenes that feature the gown take place on an uncomfortable hot day in 1935 and happen towards the beginning of the film during events that irrecoverably change each character’s life. Though it is worn with a chic, effortless ease by Knightley’s character, it was carefully chosen after previous ensembles were hastily discarded. She means to look this evocative and inviting.

The costume designer, Jacqueline Durran, also designed the costumes for director Joe Wright’s films Pride & Prejudice and Anna Karenina, both also starring Keira Knightley. Durran earned a well-deserved Oscar in 2013 for Anna Karenina. She created many copies of the green gown because the silk was so sheer and delicate that it would tear during a pivotal scene between Knightley and her co-star James McAvoy. The dress is especially gorgeous because it moves like its own creature, recalling a line from the Ian McEwan book that the film is based on that reads: As she pulled it on she approved of the firm caress of the bias cut through the silk of her petticoat, and she felt sleekly impregnable, slippery and secure; it was a mermaid who rose to meet her in her own full-length mirror.

Slippery and secure. Such beautiful words to foretell both the sweet sex that’s on its way, and the danger that’s also awaiting; everything is about to break. Every scene that Knightley wears the green dress in is fraught with impending doom, the shade lends its own sense of worry in that green is usually only used in film to detonate something sinister and bold. The shade, combined with the cut, and the way we follow the diaphanous flowing skirt towards everyone’s doom fills us with a terrible, sensual dread. It’s a wonderful sensation, to be moved so completely by colour. Atonement is a lush, beautiful film, based on a sumptuously worded novel, but it’s the green gown that will live on as the film’s true masterpiece.