The classic little black dress is simple but well tailored. Because it is easily accessorized, the dress can be dressed up or down as the occassion dictates. By not following current trends ( not a mini, midi or flamboyant) the dress maintains it's timeless quality. The cut and fabric are important factors.
Black was always worn to represent mourning. The introduction of color to the movies helped to increase the popularity of black - It was easier to color match. World War II saw a resurgence of black dresses due partly to the number of fallen soldiers and the lack of coloured fabric.
Audrey Hepburn made the little black dress famous with her role as Holly Golightly
in Breakfast At Tiffanys.