Kelly's Manhattan gallerist, Matthew Marks Gallery, says he died Sunday at his upstate New York home.
The owner of a funeral home near Kelly's home studio in Spencertown on Monday confirmed Kelly's death but could provide no other details.
The New York native spent World War II painting camouflage patterns on fake military objects produced by a special Army unit to deceive the Germans.
He moved to Paris after the war to study art. He returned to New York in the mid-1950s to begin creating the boldly colored geometric paintings that were exhibited in the Museum of Modern Art and elsewhere.
Kelly moved to rural upstate New York in the 1970s.