Ryman’s monochrome, white-on-white paintings are beautiful on screen, no doubt — see left for Exhibit A, B and C — but it’s not till you get up close that you can see they’re not really white at all. There are cool blues and mint greens pulsing behind some; others, a dash of pink. And it’s only when the works are right there in front of you that you can really get a feel for Ryman’s explorations of light, surface and material. A white square is a white square — but not when the “canvas” ranges from linen and paper to aluminum, fiberglass and Plexiglas. Robert Ryman, curated by Courtney J. Martin and Megan Witko, is both deceptively simple and endlessly engaging.