The last time I saw him, Washington's Tom Downing (1928-1985) was seated in white sunlight in his small apartment on Columbia Road NW. His shirt was white, the walls were white, the room was monk's-cell-bare. There was a teacup on the table, a mattress on the floor, and almost nothing else except one amazing painting, a painting all in red.

He despised the nonessential. By 1985, Downing had abandoned the browns and tans and blues, the idiosyncratic, strangely chiming colors that had made his reputation. By now he was content with ruled lines and with arcs and with one color only, a brilliant cadmium red. Unmixed it looked as bright as blood. Diluted it took on the pale pink of flesh. The picture, as you looked at it, began to lose its reticence, began to hint at many things -- at theater curtains, needles, crowns and sunset seas.

For a quarter of an hour, Downing stared at it in silence. Finally he spoke.

"Look," he said. "It's the last Washington Color Painting."

His body was discovered at 7:30 Sunday evening in Provincetown, Mass., in his room beside the sea. "He had been dead about a day," said James Meads, Provincetown's police chief. "There was no evidence of suicide. There were no drugs in the apartment, except for a bottle of prescription medicine, and no alcohol at all. We assume it was a heart attack. But until toxicological examinations are complete we will not know for sure."

"I am told," said Louise Downing, the painter's widow, "that they found a huge length of canvas near his bed, stapled to the floor. He always painted on the floor, but the canvas was untouched, it was completely bare. It is as if Tom were saying, 'This is all that I can do.' Or, 'I've done it all.' "

Morris Louis, the most original of the Washington Color Painters, died in 1962. His painting pal, Kenneth Noland, soon left town for Manhattan. Paul Reed has not shown in years. Howard Mehring died, at 47, in 1978. Gene Davis died in April. Downing always sought the spiritual in color, and in color only. And he never wavered. Unlike Howard Mehring, he never gave up painting. He was less whimsical than Davis, and less of a conceptualist. Downing was the most rigorous and the least baroque, as well as the least lucky, of the Color Painters.

And he was among the last.

The others kept adding to their means. Their repertoires kept growing. Louis kept inventing complicated paint techniques no one else could master, Noland started working with handmade colored papers, Mehring stayed with gesture, Davis liked surprises, but Downing would not splurge. Each time he started doing something new -- when he started painting on canary yellow grounds, or working in perspective, or painting on paper bags -- one sensed that he was searching for something to get rid of. He was not only a Color Painter. He was a Minimalist as well.

"He stayed much closer to the original idea than any of the others," says former Corcoran director James Harithas. "Every time we met we talked of the same thing -- the spirituality of color."

In his Grids and Rings and Dials -- he always worked in series -- Downing set his colors free by limiting his means. His hardness, his austerity, is in some ways misleading. His paintings may seem harsh at first, but in time they start to blossom. They change with changing light. There lurks behind their strictnesses a kind of ceaseless life.

Despite his dedication, and the beauty of his pictures -- and though the Phillips Collection gave him a small show in June -- he never really earned the success he deserved. In 1964, when Walter Hopps, a former director of the Corcoran and of the old Washington Gallery of Modern Art, began choosing artists for inclusion in the Sa o Paulo Bienal, he picked a group of winners -- Barnett Newman, Frank Stella, Donald Judd, Larry Poons, Robert Irwin, Larry Bell and Billy Al Bengston, all of them now famous. But Downing, although chosen, declined to be included. He didn't know Hopps well then. From curators and collectors he asked the same commitment, the all-or-nothing pledge, that he gave to his art.

He argued with his dealers. He once struck one in Texas who had referred to Downing as a member of his "stable." But if you loved Downing's work, and he believed in your affections, he would sell paintings to you gladly for prices that now seem ridiculously low. Gen. William Y. Smith bought a number of them, and many more were early on bought by Vincent Melzac. At other times, Downing would refuse to sell to anyone at any price -- as if he were waiting for some future when everyone would recognize the brilliance of his art.

Only last year, Ira Lowe, his Washington lawyer, succeeded in prying scores of prime Downings out of a warehouse in Manhattan where they had been stored (the bills unpaid) for 14 years.

Downing was born in Suffolk, Va., in 1928. He studied at Randolph-Macon, and later at Pratt, and then, after military service, at Catholic University, where, in 1954, Kenneth Noland was his instructor in life drawing. Later he shared a studio with Howard Mehring, with whom he helped found the Origo, a cooperative gallery at 2008 R St. NW., in 1959.

In the '60s, when he taught at the Corcoran, he was among the city's most influential teachers. The artists he inspired here include Sam Gilliam, Rockne Krebs and Michael Clark. "He was electric," Clark said yesterday. "I met him and he switched me on. One day I was a 19-year-old kid. The next day I was a painter."

"He was a quality painter, and he knew it," said Krebs. "Yet he never had consistent support here. He was always up against it financially. What happened to Tom Downing really gives me pause."

Downing was one of the Washington Color Painters -- Mehring was another, Davis was a third -- who never quite recovered from critic Clement Greenberg's arbitrary contention that Louis and Noland were the only ones that mattered. When Nolands were selling for hundreds of thousands of dollars, Downings were selling for hundreds, if they sold at all.

But still he kept on painting. "That which is properly termed art," he wrote, "is cultivated through the practice of timelessness." Downing saw in painting a path to a Nirvana where one color and one image might reveal the all.

"We're painting for the day we're dead," he told his friend, the Washington writer J.W. Mahoney. "We're painting for immortality."