I have loved the work of Njideka Akunyili Crosby since encountering her dazzling take on Manet’s “The Dead Toreador” at the Yale University Art Gallery in 2014. Since then, the 39-year-old artist, who was born and raised in Nigeria and now lives in Los Angeles, has quietly established herself as one of the most closely watched artists alive. Her works often portray herself, her husband, her friends. Their mood is sweetly muffled and intimate. They show real people in domestic interiors, sometimes partying, more often sitting, lying, embracing. For all their quietude, they are also expansive in their cultural and historical reach. Most have the scale and rich coloring of paintings but are actually works on paper. “Portals,” a diptych at the Whitney Museum of American Art in New York, was made with acrylic, solvent transfer, collage of fabric and paper, and colored pencil. The left panel shows a woman (the artist) sitting at a bare table. She appears pensive. Her body is in one of those abstracted, in-between physical states so often revealed by photographs. Pictures are stacked on the floor in the right panel, suggesting a temporary residence. But we also see a cropped wedding portrait and a television set.