Preferences on the basis of race, ethnicity, and sex — a.k.a. “affirmative action” — are found principally in three areas: education (notably university admissions), contracting (like minority set-asides), and employment (both public and private). For a variety of reasons, employment preferences — particularly in the private sector — have proved harder to uncover than the others. This is too bad, because sunlight is the best disinfectant: If preferences are exposed, they will often be abandoned, because corporate general counsels know that they can get the company into legal hot-water, no matter how much the politically correct human-resources types push them.It...