Ellsworth Kelly, on View in New York Ellsworth Kelly has been on earth for 90 years - his birthday was Friday - and he has been making abstract art for over 60 of them. Now the New York art world is treating him, and us, to a big party. His boldly colored, emblematic paintings and reliefs can be seen in five exhibitions around town. In unusually gorgeous terms, they attest to a lifelong fusion of austerity and high spirits, and a narrow yet deep exploration of pure colors and simple shapes. The shows range from a mini-survey at the Mnuchin Gallery on East 78th Street, to an array of brand-new work at the Matthew Marks Gallery's three locations in Chelsea, to a radiant exhibition of Mr. Kelly's 1971 "Chatham Series" at the Museum of Modern Art. The 14 paintings in the series have not been exhibited together since they made their public debut in 1972 at the Albright-Knox Art Gallery in Buffalo. All told, these exhibitions present 82 works produced from 1951 to 2013. They reveal an artist who is making some of his strongest work right now, at times with a decidedly erotic undercurrent. Mr. Kelly has spent much of his career romancing the vaunted monochrome in Modernist painting. He has approached this absolute without reverence or irony; it is simply the main building block of his art. For him, the monochrome has been something to particularize through shape and color, render in metal, or combine with another monochrome of a contrasting color, whether they are side by side or overlapping. The results are not so much paintings as crisp, flat objects devoid of spatial illusion. Yet the best of them are so perfectly made that we tend to forget about their physical nature, concentrating solely on their visual effects instead. Their perfection creates an aura of eternal newness that can sometimes seem antiseptic but just as often is central to their power. Whether by plan or not, these exhibitions outline the three basic ways that Mr. Kelly has used monochrome panels. Consistent with its title, "Singular Shapes 1966-2009," at Mnuchin, surveys his single-shape works. It starts with his first, "Yellow Piece of 1966," a fat yellow rectangle with two rounded corners at the lower left and upper right. It could be the daffodil-colored emblem of a fifth suit of playing cards - something between a diamond and a heart. The show's most recent work is the declarative "Blue Curves" (2009). It instantly reads as a heart shape turned on its side with its point lopped off - and as breasts or buttocks. The art historian Pepe Karmel notes in the show's catalog that the artist himself has said as much. It also resembles, fittingly, a capital B. For the "Chatham Series" at MoMA, Mr. Kelly made shaped paintings using a brilliantly obvious method: abutting two ordinary rectangles to form an inverted L. The looming vertical paintings evoke giant rulers, or details of architecture, especially posts and lintels. Each rectangle is decisively colored - red, blue, yellow, green, black or white - and their combinations pack a punch. There is a white rectangle above a black, and black above white, as well as black above red, blue, yellow or green. Red above yellow or blue. No two works have exactly the same measurements. Seen in a quadrant of spaces formed by two intersecting walls, the "Chatham" paintings encourage a dizzying process of compare-and-contrast that is less about shape than about the perception of color in terms of weight, balance and proportion. From the end of one wall, you can see one painting that is red-blue and, in the opposite direction, one that is blue-red. From another juncture, two red-blue works with completely different proportions are visible, along with a black-white and a yellow-red with similarly squat proportions but no common color. After a while the show starts to feel subtly animated, as if the blocks of color were expanding or contracting, elongating and shrinking as you move around them. The Chatham series is shown with a group of 40 small drawings and collages from 1951 whose geometric configurations presage, on a small scale, motifs later developed by artists as disparate as Sol LeWitt and Brice Marden. They also remind us that Mr. Kelly's career lacks the traditional linear development of most artists of his stature. Most of his compositions first appeared in his works on paper in the 1950s and early 1960s, which he has repeatedly mined. Now he seems interested in circling back to translate them, almost verbatim, into larger sizes or heftier materials, or both. That is the case with "Blue Curves" at Mnuchin, which is based on a 1956 collage reproduced in the show's catalog. And such translations figure prominently in the shows at Matthew Marks. Here the third use of the monochrome - one laid on top another - often dominates, and the libidinous undercurrents continue. At Mr. Marks's newly renovated 24th Street gallery, four works from 2011 employ some abrupt curved shapes from the early collages and a green and orange painting from 1964. Now the shapes are separate canvases painted red, green, yellow, or blue, laid over white rectangles. More physically defined, these bulges suggest big, cartoonish tongues. "Black Form II" (2012) in the big Marks space on West 22nd Street reiterates a double-lobed black motif from a 1962 collage. But now it is a funny, suggestive, magnificent wall relief, nearly 7 by 6 feet and over 4 inches thick, in aluminum painted a high-gloss black. The satisfying fat capital C that results looks as if one of Myron Stout's meticulous black-on-white abstractions had been repurposed by Jeff Koons, only it's better. Another standout in the big West 22nd Street showcase is "Yellow Relief Over Blue," from 2012. Basically it is a blue vertical rectangle whose bottom half is covered by a yellow almost-rectangle with a gently curved top edge. It's like sunrise from the sun's point of view. The blue and yellow are so intense and equal in strength that the physicality of the piece all but disappears. And the experience of pure, dense color is no less effective in the details. From the side, the continuation of the blue panel behind the yellow is breathtaking. It encapsulates, in miniature, the passion for color that fuels Mr. Kelly's singular art. "Ellsworth Kelly: Chatham Series" runs through Sept. 8 at the Museum of Modern Art; (212) 708-9400, moma.org. "Ellsworth Kelly: Singular Forms 1966-2009" runs through Saturday at the Mnuchin Gallery, 45 East 78th Street, Manhattan; (212) 861-0020, mnuchingallery.com. "Ellsworth Kelly at Ninety" runs through June 29 at Matthew Marks, 523 West 24th Street, 502 West 22nd Street and 522 West 22nd Street, Chelsea; (212) 243-0200, matthewmarks.com.