You can a someone from the company they keep. By the same token, an artist’s collection of fellow practitioners is suggestive of that artist’s values and ambitions.

In 2004, Alex Katz, who turns 80 next week, launched a foundation to collect contemporary art. This is something he and his wife, Ada, had been doing for some years, presenting works, for instance, to the Farnsworth Art Museum in Rockland, Maine, and the Pennsylvania Academy of Fine Arts. But the main recipient of a concentrated period of recent purchases has been the Colby College Museum of Art in Waterville, Maine, where a new exhibit shows off the bulk of his donations.

Colby is certainly a place to study Mr. Katz himself. What feels like half the square footage of what is actually the largest museum facility in Maine is taken up by the Paul J. Schupf wing devoted to Mr. Katz, stocked mostly with works donated by the artist himself. This entails more than 600 pieces and archival materials, including many important large canvases and the largest public collection of his rare, early collages. (I am the author of the catalogue raisonné of the latter, published by Colby on the occasion of their show of the collages in 2005.)

Although his gift focuses on living artists, Mr. Katz has presented a major selection of photographs by the late Rudy Burckhardt that are on view in the current show. The Swiss-born artist and his companion, the poet and dance writer Edwin Denby, were crucial supporters and inspirers of Mr. Katz during his early years of isolation. Burckhardt, too, was associated with Maine, making paintings, photographs, and films in the state, but the Katz gift is of two dozen photographs of New York City. These include his canonical shot of the Flatiron Building, tender near-abstractions that play on the rhyming of women’s fashions and street furniture, and a series of candid shots of subway riders that is, for Burckhardt, a typically dramatic in its chiaroscuro.

The Katz Foundation gifts do not follow any obvious criteria beyond the fact that their donor really liked them. Apart from one sculptor — Will Ryman, whose 10-foothigh papier-maché depicts a goofy stick figure in off-white, perhaps in a nod to his father, Robert Ryman — and a few photographers, this is overwhelmingly a show of painters, though often those who stretch comfortable definitions of that medium.

Elizabeth Murray, for instance, is represented by “Cracked Question” (1987), a large and, for this artist, unusually somber work. The multipanel construction of shaped canvases in grim tarlike hues is arranged like a question mark. It hangs opposite a mysterious abstract painting by Nabil Nahas, whose surfaces feel like shimmering coral reefs. For an artist known for his exotic, at times psychedelic color, the dark untitled work from 2001 is atypical. These works resonate powerfully with one another, and with predominantly black canvases by Mr. Katz elsewhere in the museum.

With both Ms. Murray and Mr. Nahas, it seems likely that eccentricity and chromatic restraint, which make their pieces interesting, also could have made them less welcome to private or institutional collectors. But Mr. Katz is drawn to outsiders within an artist’s oeuvre.

Similarly, Mr. Katz chose Dana Schutz’s “Abstract Model” (2007) from a recent show at Zach Feuer Gallery. This canvas, unusually small for her, comes from a series of three paintings — the others are “Male Model” and “Female Model” — in which holes are cut in the surface of the painting, with black velvet backing the space behind. These were in a show of mural-like big subject paintings — again, the outsider in the oeuvre.

On the other hand, Philip Taaffe’s “Garden of Extinct Leaves” (2006) was the showstopper at his Gagosian Gallery exhibition earlier this year. The sense of decorative overload is in marked contrast to the quietude and spareness of Mr. Katz’s language, although the artists share a bravura layering of strong colors in regimented sequence.

Several artists here recall another key feature of Mr. Katz’s painting, in which motifs are picked out on stark, single-colored grounds, whether they be abstract painters such as the Belgian Raoul de Keyser, Robert Bordo, or Robert Moskowitz, or representational artists such as Ena Swansea or Ellen Phelan, whose “Mt. Tacoma Tulips in a Chinese Vase III” (1999) is painted in a blue-gray monochrome.

While some of the artists are foreign-born — such as Mr. Nahas, who is Lebanese; Mr. Bordo, who is Canadian; the German Justen Ladda, and the Italian Francesco Clemente — this is by and large a New York-centric group, and reflects Mr. Katz’s social circle. An exception to this rule is Britain, where three of the artists live and work: Julian Opie, Gary Hume, and Merlin James.

These very different artists, who are all in their 40s, each relate to some aspect of Mr. Katz — whether his style, subject, or attitude. Mr. Opie plays stylish conceptual games that personalize schematic outlined figures, as in “Ruth With Cigarette #5” (2005-06). Mr. Hume pushes flat areas of paint to extremes of near mute décor, as in “Fashion” (2004), which applies lush stripes of enamel paint on an aluminum support. Mr. James shares a similarly odd mix with Mr. Katz of being personally invested in his images and aloof from them. A critic as well as a painter, he has written several essays on Mr. Katz.

A couple of American artists share Maine as a motif with Mr. Katz: Susan Shatter, who had been a student of his at Skowhegan in 1964, captures the drama of the rocky coastline in “Wave” (2000), a large-scale watercolor. Another is Lois Dodd, a fellow student at the Cooper Union with whom he bought the Maine farmhouse he still lives in each summer. Through his generosity to Colby, Mr. Katz ensures that his work will ever be surrounded by diverse and lively friends.

Until October 28 (4353 Mayflower Hill, Waterville, Maine, 207-859-4353).