
While a number of the costumes constructed for the film production went off the rails in terms of historicality, the mourning dress worn by various characters throughout was generally very period-appropriate (which is good since Scarlett's flaunting the mourning attire is an important part of her character and the story).
The image here (and click it to see it up close in all of its watercolor glory!) was found at Dial B for Blogger, a Spanish-language blog that features others of Plunkett's designs in a post honoring Gone with the Wind's 70th anniversary.