ALMA THOMAS, “Snoopy Sees Earth Wrapped in Sunset,” 1970 (acrylic on canvas). | Smithsonian American Art Museum, Gift of the artist; Courtesy Studio Museum in Harlem   AT A TIME WHEN MOST ARTISTS are in the sunset of their careers, Alma Thomas (1891-1978) was on the rise. Recognized for her expressive abstract paintings, her exuberant use...