A small but wondrous Alma Thomas retrospective at the Studio Museum in Harlem put me in mind of a desert plant that spends all year as an innocent cactus and then, in the middle of the night, blooms. Thomas, who died in 1978, at the age of eighty-six, was a junior-high-school art teacher in Washington, D.C., whose own paintings were modernist and sophisticated but of no special note until she retired from teaching, in 1960, and took up color-intensive abstraction. Her best acrylics and watercolors of loosely gridded, wristy daubs are among the most satisfying feats (and my personal favorites) of the Washington Color School, a group that included Morris Louis, Kenneth Noland, and others associated with the prescriptive aesthetics of the critic Clement Greenberg: painting shorn of imagery, the illusion of depth, and rhetorical gesture. Wielding brushes, Thomas eschewed the group’s signal technique of working strictly with stains of liquid paint on raw canvas, proving it inessential to an ordered glory of plangent hues. She seemed to absorb in a gulp the mode’s ideas—rational means, hedonistic appeals—and to add, with no loss of formal integrity, a heterodox lyricism inspired by nature. The boldly experimental work of her last years suggests the alacrity of a young master, but it harvested the resources of a lifetime.

Thomas, who was African-American, was born in Columbus, Georgia, in 1891. Her father was a businessman, her mother a dressmaker. She had three younger sisters. In 1907, the family moved to Washington and took a house in a prosperous neighborhood, in which she lived for the rest of her life. She concentrated on math in high school, and dreamed of becoming an architect. Unsurprisingly, given the time’s odds against her race and her sex, in 1914 she found herself teaching kindergarten. In 1921, she enrolled at Howard University as a home-economics student, but gravitated to the art department, newly founded by the black Impressionist painter James V. Herring, and became the school’s first graduate in fine arts. Later, she earned a master’s degree from Columbia University’s Teachers College and studied painting at American University, where she encountered Greenberg’s doctrines.