Early on in the 2014-15 season, the Milwaukee Rep staged "The Color Purple." It's a show actress Felicia P. Fields knows very well; after all, her turn as Sofia in the Broadway musical scored her a Tony nomination for Best Performance by a Featured Actress in a Musical back in 2006. It's another familiar show, however, that brings Fields back to Milwaukee: "Low Down Dirty Blues," a celebration of classic blues at its deepest and dirtiest.