“I can line the paintings up in my studio as I paint them and see the color graduations while I’m doing it,” the abstract artist Pat Steir, now 81, said of her latest commission, the largest site-specific installation she’s ever done. Inspired by the circular shape of the Hirshhorn Museum’s inner gallery, Steir decided to create a color wheel with her trademark waterfall paintings—works in which pours of paint cascade down monochrome backdrops. Here Steir’s waterfalls take on the visible spectrum. —C.J.F.