Oliveira Ce'zar, a painter of high skill who was trained in Buenos Aires but now lives in Paris, is showing his mystery-filled pictures at Robert Brown Contemporary Art, 1005 New Hampshire Ave. NW. Ce'zar paints interiors. There is almost nothing there.

Sunlight from an unseen source falls upon a plaster wall, or shines underneath a door, or illuminates a stair. There are no carpets on the floor, no pictures on the walls. Ce'zar's rooms are empty. One never sees a table or a sofa or a chair. Still, something haunts his pictures. His spaces have the look of spaces that are looked at. One wants to turn around to see if someone's there.

That someone might be daydreaming, or gazing inattentively at that beam of light sliding down the wall. That quality of hauntedness is heightened by the color, or perhaps the lack of color, of Ce'zar's meditative pictures. They are almost black-and-white -- almost but not quite. Hints of absent colors, of yellows, blues and browns, glint behind their grays. They look like pictures on a color television set once you've tuned the color down until it's no longer there.

The 17th-century Dutch often painted empty rooms. So, too, did Vilhelm Hammershoi (1864-1916), the Dane whose works were shown here at the Phillips a few years ago. Ce'zar's paintings next to theirs feel a bit surreal. The scale is just slightly off, those stair treads are too large, those ceilings are too low. His are spaces one might see not in life, but in dreams. His paintings look just right in Brown's white-walled skylit gallery. They will be there through May 20. Color School Tradition

Though unexpected colors and rigorous geometries have been wed in abstract painting here since the 1950s, rough, organic forms have of late attacked the Euclidean austerities of Washington color painting. Dark plants spread their heavy leaves in the art of William Willis and the drawings of Jeff Spaulding, and vines as thick as those on which Tarzan swung twist through Patrice Kehoe's paintings.

The jungle has invaded, too, the recent art of Michael Smallwood and that of Patrick M. Craig.

Michael Smallwood's paintings, now at Addison/Ripley, behind the Phillips Collection at 9 Hillyer Ct. NW, adhere with such obedience to color school traditions that they'd seem almost timid were it not for the jagged forms of waves, or leaves, that claw them now and then.

Smallwood cleaves to flatness. He likes straight lines and right angles and thickish bands of color that call to mind, though distantly, those of Morris Louis and Gene Davis. His use of layered colors -- say, bright magenta roughly brushed over orange-red -- suggests Jacob Kainen's. The big right-angle triangles that jut, from top or bottom, into his abstract paintings recall the color-bearing triangles of Kenneth Noland's "Chevrons." Smallwood's works would evoke safety were it not for the aggressive plant forms that attack their calm.

The picture he calls "Truce" is based on a diagonally divided rectangle flanked by colored bands. But its symmetry is overwhelmed by the pointed wave of red that sweeps in from the right. So bright is that bright red, and so fierce is its invasion, that the painting comes to feel less like truce than war. A number of his pictures are weakened, so it seems to me, by the arbitrary verticals that slice them into pieces. Those lines are sometimes painted on; sometimes they're the shadow lines of his butted diptychs. What logic they obey is external to the painting. I don't know why they're there. His show closes on May 10.

Patrick Craig's sleekly polished oils, now at the Midtown Gallery, 1630 Connecticut Ave. NW., are more varied, more mysterious. His surfaces are divided, by arcs, straight lines and circles, into discrete, hard-edged shapes, but his shapes are never flat. Some are hollowed, others bulge. The concentric arcs appearing at the upper left of "Feeder" have become, through modeling, a serpent's shining coils. His circles become portholes -- they might offer up a glimpse of some tilting, colored sea. Growing from between his intersecting arcs are daylit, living things -- say, the snapping beak of some strange bird, a rhino horn, a talon, a pair of pointed breasts.

In the painting "Beast 'n' Beauty" (1986), three slender orange fingers, with pointed nails painted brown, are being stroked with touching tenderness by a pair of bright green claws. The picture also offers a stretch of speckled pelt, and what seems a distant tree line, and a rough stone wall. The viewer is not sure what this picture means, but there is much to look at, and the work is filled with sun. By his modelings and punctures and eerie evocations, Craig has started pushing Washington color painting into unfamiliar realms. His show closes May 24. Nick Fennel at Ewing

Nick Fennel, whose pictures are on view at Kathleen Ewing, 1609 Connecticut Ave. NW, is another color painter who likes the compass and the T square, and the reassuring order of circles, diamonds, squares. His show is titled "Local Color," but its color is not Washington's. Instead his pictures call to mind sunny California or the mists of the Northwest.

Fennel lives here now, but he was trained, as an architect, in Long Beach, and then moved to Seattle, and the climates of those places still may be detected in his light, attractive art. In his "Lyricists and Composers," one feels the northern sun as it might appear through wave spray and through sea mist. In his "Freer Expression" (the title might suggest the Freer Gallery of Art), the softness of the colors is made costly and exotic by the sort of scattering of gold that one might discover on an oriental scroll. Fennel's art is never harsh. Its mood is always airy. His show closes May 10.