Olivia Wilde's Wedding Guest Attire Included a Backless White Maxi Dress

While everyone knows that you should never wear white to a wedding, Olivia Wilde just broke the cardinal rule of wedding guest etiquette when celebrating a close friend’s big day — and she was sure to call herself out for it in the toast.

On Sunday, the actress and director shared a snap detailing the white gown she wore when attending the nuptials of Colton Underwood and Jordan C. Brown in Napa Valley over the weekend on her Instagram Story. In the photo, Wilde posed with her back towards the camera to show off the Nili Lotan dress’s backless design, which featured a lower back-skimming dip and two dainty spaghetti straps. A matching white umbrella and oversized black sunglasses served as the look’s sole accessories, and Olivia wore her caramel hair down in soft waves with a middle part.