The Dress

When examining the wardrobe of a femme fatale, the most oft picked color is black. 

Consider the following:

Ava Gardner - The Killers

Rita Hayworth - Gilda

Joan Bennet - Scarlet Street

Ann Savage - Detour

Lizbeth Scott - Too Late for Tears

The femme fatale is the antithesis of the damsel in distress or "good woman". She is not without sin but without remorse in her role as man's ruin. Her sexuality is her weapon. Black, then, would be the most appropriate shade for her wardrobe.

Why, then, would costume designers throw the audience for a loop by dressing the femme fatale in white?

Lana Turner - The Postman Always Rings Twice

Jane Greer - Out of the Past

Barbara Stanwyck - Double Indemnity

Yvonne DeCarlo - Criss Cross

With so much focus on the black dresses of femme fatales (or female characters in general), the audience comes to expect the dangerous female as black widow. She can wear no other color, especially not white. White is meant as innocence and purity; certainly not the characteristics of a femme fatale. However, they were once virtuous women who have been scorned. Once those virtues are lost the associative color is black. We see this in Lana Turner's character in Postman

After murdering her husband, she wears black. In Out of the Past, it is the same ideal. Jane Greer's character becomes more volatile and murderous and her wardrobe darkens. In Criss Cross, Yvonne DeCarlo wears both colors throughout the film. On one level she is ruthless, yet there are moments where she can be more damsel in distress. Her character, herself, can't decide which path is the right one.

Femmes Fatale are the most fascinating because their characters are so complex. You want to hate her but you can't help but empathize with her.