Mike Figgis’ “The Blues” series for PBS chronicles an important shift in audience, then ignores it. “The accretion of whites in Mr. Figgis’s film reflects both the majority of the public-television viewership as well as the largest audience for the blues these days. The London blues-rock stars who heard the music as teens in the 1950’s and 60’s — like Eric Clapton and Eric Burdon, who are both featured in Mr. Figgis’s film — exposed it to the rest of the record-buying world: suburban kids who now keep it alive. It’s a sad fact that ‘The Blues,’ devoted to the cumulative power of a cultural phenomenon, tends to ignore the racial shift in the music’s fans. Such a lack is like overlooking a roasted tree stump that was rocked by lightning.”