Kerry James Marshall made this painting in 2018, the year after his career retrospective, “Mastry,” attracted large crowds and garnered rave reviews in New York, Los Angeles and Chicago. Most artists who get this kind of mid- or late-career attention flounder for a bit. “Untitled (Underpainting),” which is owned by Glenstone, feels like an unusually taut and tough-minded response to that period of sustained applause. It’s a very self-assured painting. Consider just the mechanics. You’re looking at a picture of a large gallery divided in half by two parallel white partitions. The painting’s two halves are not quite mirror images: the figure closest to us on the right, for instance, is a man, while the equivalent figure on the left is a woman. But look closer and you see that the arrangement of gallery-goers on both sides is approximately the same. If that makes you think of a Rorschach test, that’s probably Marshall’s intention: He is always interested in what the viewer projects. Speaking of viewers, there are dozens of them spread through the divided gallery, including two groups of schoolchildren. The paintings in front of them are big, museum-ready canvases, like the one you’re looking at, which measures 10 feet by 7. Most of Marshall’s paintings are vividly colored. This one, however, is in shades of grayish umber, evoking (as the title reinforces) a painting yet to be finished. “I’ve always been interested in unfinished underpaintings,” Marshall said in a recent interview, “like Leonardo’s ‘Saint Jerome in the Wilderness.’ ” It was from just such works, he said, that he learned how paintings were constructed. If you can see how something is constructed, you can see more easily how it might have been different. And that is something I suspect Marshall thinks about every day.