When most people worked outdoors, suntanned skin was disdained as the mark of a low-status laborer. Light skin, in contrast, was prized as a mark of wealth; only the rich could afford to protect their skin by remaining indoors or else carrying parasols. Later, when jobs migrated to factories and offices, lighter skin became common and vulgar, and only the wealthy could afford to lay around soaking in the sun.
Analagous to fitness signaling.
