A decade ago, Alex Katz, a painter known for his large and vivid portraits, had a show of his early paintings from the 1950s called Brand New and Terrific. During the many appearances he made for the show as it moved from museum to museum, Katz often told a story that explained how his early work had morphed into his mature, muscular style: In the 1950s, in a group show in New York, one of his paintings was hung next to a work by Beauford Delaney, an artist who came to the city as part of the Harlem Renaissance, and eventually moved to Paris after the war. Katz, still smarting at the memory, told interviewers that Delaney’s brightly colored painting had blown his painting off the wall. He was so frustrated that he vowed never to let it happen again. (The result was a quantum leap for Katz.)