An English artist who chased the rainbow's subtle colors

Matisse said color must not ``simply `clothe' the form: It must constitute it.'' This observation could almost have been the touchstone for the long painting career of the English artist Winifred Nicholson (1893-1981).

The Tate Gallery is staging the first sizable retrospective of Nicholson's paintings (through Sunday). It is a show that cannot have been easy to put together. A major retrospective suggests the honors of importance and history - both of which Nicholson, in her approach to art, tended to avoid.

Masterpieces, she felt, were for other artists, and she scarcely ever dated her works. In addition, most of them are of modest size. A feeling of simple domesticity sometimes seems to hover over her aims and achievements. These pictures belong in low-ceilinged rooms, in people's kitchens and sitting rooms. They do not look entirely at home in large public galleries. Such a context emphasizes a certain prettiness that was an undoubted risk in work that concentrated largely on the loveliness of the world and was composed with a light touch and palette.

This said, however, the refreshing originality of Nicholson's paintings certainly deserves the Tate's accolade.

Coinciding with this show - which will travel to five other venues in Britain after the Tate - is the book ``Unknown Colour'' (edited by Andrew Nicholson, her son, and published by Faber & Faber), which gathers her writings together with more paintings, well reproduced in color.

What emerges from exhibition and book is a painter with a rare, intuitive sensitivity to color. Colors to her were not only the relating qualities that constitute light, but the scarcely explored essence of painting itself. Her pursuit was to paint light. Like Matisse, she wanted her paintings to give out their own luminosity - and one is almost persuaded that they do, though of course paintings can only reflect light.

She possessed, and never lost, a child's love of nature - particularly of its bright, iridescent aspects, and this love fed her deep appreciation and expression of both light and light's vast spectrum of colors.

The physical qualities of color clearly fascinated her; she studied - and endeavored to transmute into paint - the translucency and brilliantly living hues of flower petals, the reflective transparency of glass, the opalescence of shells, and the arcing, edgeless bands of the rainbow.

Her pictures are quick, painterly, hopeful. They are disarmingly unpretentious, too: The instinctive takes over entirely from the theoretical. If they are in danger sometimes of being fey, her sensitivity to the delicate details of nature is generally translated into brushwork of stimulating vigor and directness.

Her writing shows another side of her character: fascination for the play and potency of words and theories. She was particularly intrigued by the colors barely perceptible at the peripheries of the spectrum, where red disappears into infrared and violet into ultraviolet.

She peered with wonder at the astonishing colors that things appear to possess under microscopes. And she had a lifelong delight in prisms, which culminated in her last years in both an exchange of letters with Canadian physicist Glen Schaefer and in an astonishing group of paintings, some of which had a rough force unprecedented in her work. They were based on the bright colors seen on the edges of everyday objects when viewed through a prism.

Nicholson's art cannot be appreciated fully unless it is understood that she was a visionary painter. The artist had a capacity for perceiving something transcendent in the ordinary. Her typical motif of flowers on a windowsill is a commonplace of home. But its visionary qualities also suggest that she thought of her painting as an escape from the mundane.

The visionary quality of Winifred Nicholson's art was a fact emphasized by English abstract artist Ben Nicholson in their correspondence. She was his first wife, and although their marriage ended in the 1930s, it is clear from their letters in ``Unknown Colour'' that they were held together by unbroken threads of art as well as family for the rest of their careers.

These letters are both moving and revealing. Ben clearly valued her contribution, not just to his own art's development, but as a painter in her own right. Their exchanges were along the lines of an old divide: the classical vis-`a-vis the romantic, the rigors of form and line vis-`a-vis the freedoms of color.

Winifred knew her weakness: She knew that in giving everything to color she was abandoning the more structured, formal aspects of painting - aspects in which Ben was notably strong.

Her ``abstracts'' in this retrospective, painted in the '30s when she was most in touch with the Contructivist movement, fail for the most part to contain her special ``vision.'' There are a couple of striking exceptions - one of which she apparently repainted in the 1970s with much more vital color. And it was only in her last years, equipped with what she called in a William Blake-ish phrase her ``friend Prism,'' that she seemed to a certain extent to grasp that elusive thing called color so boldly that it gained in her paintings sufficient strength in itself to become - or at least act for - form.

Earlier she had thought such a rapprochement would mean she would have to be two people. But this surge of experiment adds a rigorous chapter to many years of inspired painting, and is still true to her singular vision.