> For decades, the color film available to consumers was built for white people. The chemicals coating the film simply weren't adequate to capture a diversity of darker skin tones. And the photo labs established in the 1940s and 50s even used an image of a white woman, called a Shirley card, to calibrate the colors for printing. post 
Even a properly exposed B/W image will find contrast in only the specular reflections (glare) of the black body. wikipedia
The post cites the long and appropriately technical article, Looking at Shirley, the Ultimate Norm:
Colour Balance, Image Technologies,
and Cognitive Equity
by Lorna Roth of
Concordia University. pdf
Physics. The eye sees a much larger range of light than film. Gamma and exposure represent a compromise that we learn to see as representative of the world.
(The ratio of diffuse to specular reflection favors the fair skin. See the image where both children are equally shiny.)
Economics. Images and especially color images must look good to the buyer. Amateur film and processing struggles to make skin look correct enough in snapshots. Paul Simon sings of this in Kodachrome.
Equity. The industry safely ignored minorities until Japanese became an important market. Curiously advertising images of dark wood furniture and chocolates illustrated the limitations of physics and economics before representation of blacks became an issue.
See also ID-2 Controversy where another photographic industry leader puts economics ahead of equity.