You don't think of white as a color that shocks the eye. But a dab of white oil paint on the surface of a painting can engage the senses, the emotions, and the intellect.

It can be a flash of light, a hint of transcendence. Or it can be aggressive blankness, a concealing fog, a blanket of snow, turbulent water, a light so bright that we cannot see anything else.

Richard Pousette-Dart and Walter Elmer Schofield, the subjects of two ambitious current exhibitions, were very different artists, with very different goals and visions. But in both shows, the works with white in the foreground are the most compelling, and very likely the artists' finest.

The first thing you see at the Philadelphia Museum of Art's exhibition "Full Circle: Works on Paper by Richard Pousette-Dart" is Beyond the Moon, from 1990, one of several of the artist's works recently acquired by the museum. Its surface is dark, crosshatched, and scribbled upon with pencil and charcoal, and even the circle that we take to be a full moon seems to be behind some sort of a gray mesh. Yet right on the surface of the painting are dabs of white paint that make it luminous.

Chronologically this work should be at the end of the show, but it is easy to understand why curator Innis Howe Shoemaker put it first. It shows both the cosmic perspective the artist developed in his last decades, and the dense, fine, nervous line characteristic of his work from the beginning of his career.

Pousette-Dart, who was born in 1916 and died in 1992, is remembered as one of the founding members - with Jackson Pollock, Willem de Kooning, Mark Rothko, and others - of the post-World War II New York School, which is credited with putting American art on the world map. These pioneering artists certainly shared ideas, notably a sense of improvisation and fascination with chance. At their best, they produced works that are not pictures but presences; they have coherence and impact, but no obvious subject.

Yet when you look at the works Pousette-Dart produced during the late 1940s and early 1950s, the moment this art was exploding on the scene, they seem irresolute. Some of them were developed from a surrealist approach of drawing almost at random, and seeing where it led. Even more than most doodlers, Pousette-Dart did not know when to stop. He layered pencil and ink, translucent and opaque watercolors to make stains, patterns, evocative but non-specific shapes, and then, sometimes, he scratched part of them off. He seems to have done everything you can do to a piece of paper.

In many cases, he overlaid a grid on all this chaos, which makes some of these pieces seem like a view through a window, or a stained glass window or mosaic pattern. These grids form a scrim of self-consciousness. They seem to take the painter, and the viewer, out of the action.

But in 1955, he did one of these works, Reflections on a Pond, using a simple palette of graphite, to make a grid, circle, and other shapes, and then added white oil paint that seems to jump off the surface. It's only paint, but it carries a hint of some deeper reality. In the mid-1970s, he returned to this idea to produce the white and graphite works that are the reason to see the show.

Here, the fussy, obsessively complex drawing style coheres to produce works both spiritual and scientific, meditations on cosmos and microcosm. A notebook on display contains his thoughts from 1981: "black and white is the guts of all color/ the structure, base, body, bottom line/ the extacy of abstract beauty."

The white in "Schofield: International Impressionist" at the Woodmere Art Museum mostly depicts snow - not often seen in the paintings of the French impressionists.

Walter Elmer Schofield (1866-1944) was a Philadelphia landscape painter who divided his time between the U.S. and Europe. When he painted in England and France during the summer, his works seem very sunny, charming and "impressionistic," but back in Philadelphia in the winter, painting the Wissahickon and other nearby bits of wilderness, things are tougher and more interesting.

While the show emphasizes Schofield's cosmopolitan career, and widespread, if long gone, popularity, Schofield seems a quintessential second-generation product of industrial Philadelphia. His father was a manufacturer; he went to the Pennsylvania Academy of the Fine Arts, then on to study in Paris. He was a member of the generation that sought to bring refinement to a tough industrial city, the generation that produced the Benjamin Franklin Parkway and what the architect George Howe called the "Wall Street pastoral" of Chestnut Hill. In the few instances where there are people in the paintings, they literally fade into the landscape. The modern world that made Schofield's career possible is almost wholly absent.

Schofield clearly liked painting snow scenes, and they seem to have been popular with collectors. In paintings such as Hill Country (1913), which has long been in Woodmere's permanent collection, the snow allows the composition to be bolder and more abstract, highlighting the landforms even as it obscures rocks and plants. Other works, such as Wissahickon in Winter (circa 1920) present the snow as an optical phenomenon. Strokes of brilliant white are modulated by the blue of snowblindness, something that Schofield must have experienced painting outdoors in winter, along with grey shadows and even bits of green and red. It is a bravura performance that reminds us of a physical fact. To see white is to see all colors at once.

Art: TWO MASTERS OF WHITE

"Full Circle: Works on Paper by Richard Pousette-Dart," through Nov. 30 at the Philadelphia Museum of Art, 26th and the Parkway. Hours: Tuesday–Sunday, 10 a.m.–5 p.m.; Wednesday and Friday, main building open until 8:45 p.m. Adults, $20; 65 and over), $18; students with valid ID, $14; 13–18, $14; 12 and under, free. 215-763-8100 or philamuseum.org.

"Schofield: International Impressionist," through Jan. 25 at Woodmere Art Museum, 9201 Germantown Ave. Tuesday-Thursday 10 a.m.–5 p.m.; Friday 10- 8:45; Saturday 10–6; Sunday 10–5. Adults, $10; 55 and over, $7; children and students with ID, free. 215-247-0476 or woodmereartmusem.org.EndText