Syreeta McFadden, writing for Buzzfeed:
Most photographers — my parents, the Olan Mills studio — didn’t have that control. Unless you were doing your own processing, you took your roll of film to a lab where the technician worked off a reference card with a perfectly balanced portrait of a pale-skinned woman.
They’re called Shirley cards, named after the first woman to pose for them. She is wearing a white dress with long black gloves. A pearl bracelet adorns one of her wrists. She has auburn hair that drapes her exposed shoulders. Her eyes are blue. The background is grayish, and she is surrounded by three pillows, each in one of the primary colors we’re taught in school. She wears a white dress because it reads high contrast against the gray background with her black gloves. “Color girl” is the technicians’ term for her. The image is used as a metric for skin-color balance, which technicians use to render an image as close as possible to what the human eye recognizes as normal. But there’s the rub: With a white body as a light meter, all other skin tones become deviations from the norm.