Ellsworth Kelly Serpentine Gallery, London W2, until 21 May
Clarity, elegance, austerity, grace - you would hardly think these qualities went with brash and even eye-popping colour but so it is with the painting of Ellsworth Kelly. Kelly is a pioneer of American abstraction, a fabled figure, an early minimalist. He will be 83 this year. While contemporaries such as Ad Reinhardt, Donald Judd and Dan Flavin are all long gone he is still avidly picking over the potential of a few shapes and a handful of hues in a small town just far enough from New York to discourage predatory visits from the art world. He could almost be an advertisement for the benefits of peace and hard work.
Peace is certainly the characteristic atmosphere of his shows. Visitors slow down, drop their voices. That this should be the case when the colours are so full-volume - yellow, red, acid green - is part of the communal pleasure of his art;
everyone appreciates the paradox, how this loud colour can possibly inspire a zen-like hush, and the way it hints at a genial humour at work.
For what is so calming about lime green next to orange next to violent yellow? Quite a lot, it seems. First of all, the three colours starring in this recent work are confined to separate panels, one above the other, a stacked triptych. They do not mix, even though they meet. Then the big stretch of orange in the middle becomes a kind of go-between, a mediator, finding the common ground between the smaller green and lemon panels. For those colours do have affinities, of course, which this piece brings forth; and both have chromatic connections with orange. You stare at all this going on - the naming of colours, as the composer John Cage once put it - and it feels like a strong continuous song.
Plain chant, perhaps; very rich, but very structured and simple. In no time a sense of order descends. Most minimalist art has that effect, the obvious consequence of paring things; but it can sometimes come across as compulsive neatness. Kelly's art doesn't want to be tidy and complete. He's after headier pleasures. The oddly shaped canvases he has been developing since the Fifties - kites, arcs, parallelograms, triptychs, squares and rectangles layered one over the other - aim to keep on unfolding before you.
Hence the way people slacken their pace, observing the unexpected behaviour of his art. The way a red square with one curved edge will seem to jump out of its skin, releasing a tide of redness. The way a pearl-grey rectangle will seem to pass more slowly in front of a black rectangle than the other way round (his works often come in complementary pairs). How a painting's shape, say a parallelogram, may seem to give it forward thrust, sending it flying along the wall; or the addition of a curve layered against it will draw that form back, holding it tense as a bow.
Kelly had his first abstract vision at 12: an arrangement of red, black and blue seen through a distant window; actually just curtains, a fireplace and a couch, but he was entranced. You get that same effect, serendipitously, at the Serpentine Gallery - coming round corners and through doorways, seeing his paintings fragmented and framed. Which is reportedly how it all begins - sunlight on a roof, a cheek's curve, a shadow, a leaf, from which he preserves a fragment; something fixed in drawings but transformed in paintings that distil the source without ever describing it.
Kelly's sources were closer to the surface in the past. South Ferry drew into harbour, and drew out again, tracing an elegant cross. Night lights reflected in the Seine became striations in black and white. Lately, however, his observations go much deeper; as if he is remembering old art and not new sights. The lime-lemon-orange triptych apparently recalls a particular Rothko. White paintings go back to Malevich, and early Kelly himself. A beautiful blue-on-green relief may bring Richard Diebenkorn's Ocean Park paintings to mind. And there is always a love of Matisse.
A big yellow-on-red relief is full of Matissean joy, and indeed anyone standing against it becomes as sharp as a cutout. Kelly says he was thinking of the way a wheatfield will glow beneath a blazing sun and there is that sense of land and sky nearly inevitable with horizontally divided abstracts. But although certain associations may press forward - beaches, meadows - they are neither first nor last among one's experiences of the work. Sheer intensity of hue puts you on the spot, asks for your response, puts form and scale of colour before everything else.
This is partly what clears and relaxes the mind; for the first appeal is purely optical, the second entirely abstract. Which doesn't mean that all Kelly's paintings act upon you in the same way; you can certainly like one more than another. Some of his shapes seem deliberately awkward. Some of his colours - school maroon, say - can't help being hideous in some people's eyes.
But compare Kelly with Rothko. It is vital that Rothko's maroons should be apocalyptic and his yellows numinous; his values are spiritual. Kelly wants to let colour be itself, do its own thing. And a basic pleasure of his art is that it occasions quite simple feelings about colour - how hopeful is yellow, how soothing black can become when placated by white, how Proustian is that marvellous blue that can take you to Greece or the ocean in an instant.
Theory attaches itself to Kelly like convolvulus. Over the years, it is true, he has found many ways of displaying flat painted surfaces as not entirely paintings and not quite sculptures. At the Serpentine, his freestanding Brancusi-like columns are so slender and flat as to appear almost 2-D; his reliefs are literally mounted at a distance to the wall so that shadows emphasise their form and become part of the work.
But even if there is a subtle philosophy at play here, the works themselves shrug free of dead-handed theory. In his eighties, Kelly seems more refined than ever, more serene. The most beautiful piece here is less late Beethoven than Matisse and all about the grace of curves. A white curve lies against a white square and the narrow edge between them, carrying the light, is exquisitely radiant.
As you move, the light moves. The concept is simple and self-evident. It is also obvious that the piece is midway between painting and sculpture. But the joy of it lies elsewhere and is far more exceptional - the dreamy white rainbow Kelly makes visible, with the barest means, in the mind's eye.
