"Art is something you look at," scolded the Minimalist sculptor Donald Judd in 1966, dismissing the work of a European artist who had offered an empty, whitewashed gallery as a one-man show. Little did Judd know that a generation of American gallery-emptiers who called themselves Conceptual artists would soon be on the rise.

Sol LeWitt is usually credited as the inventor of the label Conceptual Art, and his spare wall drawings and attenuated modular sculptures made him a vital link between Minimalism and the new, dematerializing trend. Yet from the start he was careful to hold his middle ground. As Conceptualism grew ever more invisible, he stayed with an art you could look at, and even gave it a memorable allure.

That allure has grown over time and is very much evident in the artist's vibrant new paintings, on view in two Manhattan galleries. The work is the outcome of a long development. In the late 1960's and 70's, Mr. LeWitt created austere graphlike linear designs in black ink on white walls. Then in the 80's he floated geometric shapes drawn in colored inks over dusky blue and violet fields. These murals -- executed by assistants from Mr. LeWitt's designs and whitewashed over at the end of a show -- had a sensuous, clarified presence, at once spacey and classical in feeling. The new works -- large gouaches on paper at Gagosian Gallery, small gouaches at 128 Gallery -- are all straight from the artist's hand. In them color has become more prominent and active, and geometric forms have been traded in for a sinuous, all-over painting that seems like a hybrid of calligraphic gesture and mechanical patterning.

Both groups of work limit themselves to a palette of red, yellow, blue, black, white and gray -- Mondrian's colors, as it happens -- within which complementaries emerge here and there where strokes overlap. The strokes themselves, long and often unbroken over their course, are applied with uniform, narrow brushes (larger for the larger works, naturally, smaller for the smaller) and form distinctive patterns from painting to painting.

In a dozen of the small pieces, for example, the strokes descend vertically, gently undulating like plastic strip curtains hung in a breezy doorway. Elsewhere, they flow horizontally or in wavy diagonals. In the works at Gagosian, patterns are painted on top of patterns. Their built-up tangles suggest spatial depth, and their swells and waves have an Op Art-ish retinal throb.

"Conceptual art doesn't really have much to do with mathematics, philosophy, or any other mental discipline," Mr. LeWitt once said. He spoke for himself (a number of his colleagues disagreed), but he has never made work that better illustrated his point.

These paintings manage to be personal without having a jot of personality and vivacious while following a near-rote format. In the end, in their detached but romantic way, they point to the native radiance of the material of art itself -- color, line -- and how it does what it does, which works out to be not all that much and yet a lot at the same time.

The new work isn't the kind of epiphany that Mr. LeWitt's move into color was over a decade ago, but it's a jump, and with its catchy rhythms and cool, noncommittal exhilaration, it offers a visual lift-off from the everyday without going too far from solid ground. That ground is, of course, the artist's familiar middle terrain between the look of art and the idea of art. Once again, he navigates it eloquently.

Sol LeWitt's paintings remain on view at Gagosian Gallery, 980 Madison Avenue, near 76th Street, through Oct. 21, and at 128 Gallery, 128 Rivington Street, on the Lower East Side, through tomorrow.

Photo: One of the small gouaches by Sol LeWitt on view at the 128 Gallery. (128 Gallery)