The late Robert Ryman (1930–2019) was called a minimalist, a monochrome painter, and a conceptual artist. He preferred the term “realist” to minimalist because he presented materials as they were. And while he favored the colors white and off-white, to him they weren’t monochrome. In a 1971 interview with Phyllis Tuchman, in Artforum, he said, “I don’t think of myself as making white paintings. I make paintings; I’m a painter. White paint is my medium. There’s a lot of color involved. I don’t mean color like red, green, and yellow; but, color, in that sense.” Of the square format, he said, “that seems to be the most perfect space.” Clearly, Ryman set parameters for his paintings, which he saw as explorations of light and space. At Zwirner, Ryman’s lesser-known early works are on view, including a selection of rarely seen pieces on raw linen and a few of his paintings-within-paintings. This is a don’t-miss show. —Jeanne Malle