The Second Challenge, by MacKinlay Kantor (epub/Kindle)
Chuck Noel has blue eyes, from which the pigment seems to have been washed by dry heat until only the blanched, toughened iris remains. He wears his hat on the back of his huge head, and in the hollow of his left arm is a light shoulder-holster with a spring clip. A double-action Colt .45 reposes there.
Occasionally, of course, he has need to remove the Colt from beneath the spring clip, very hurriedly. But that is never in the Little Owl cafe...