THROUGH THE AEGIS of a 1991 artist monograph and a major traveling exhibition, the art and life of the important but little known American painter William Henry Johnson (1901-1970) was rescued from almost complete obscurity. What made this act of cultural retrieval all the more noteworthy was the introduction into the modern American art canon of over one hundred oil, tempera, and watercolor paintings that epitomize a provocative merging of World War II-era modernist aesthetics with African-American cultural sensibilities.