 One could argue that so long as only black artists sing it, the opera is circumscribed almost as a period piece. After all, you don't have to be Russian to sing Mussorgsky's Boris Gudunov, and no opera could be more Russian than that. For help in figuring out what to make of Tibbett's Porgy, I conferred with John McWhorter, whose New York Times columns regularly deal with culture and race.