Soberly dressed, unflashy, and a trained classical musician, in the golden age of the music business Milt Okun stood out by not standing out.  His legacy does that for him.  He discovered and launched John Denver, and mentored him throughout his career.  He created arrangements for "Peter, Paul and Mary" that the trio performed for half a century. He brought Placido Domingo a crossover career that made him an international star beyond the world of opera.  He founded Cherry Lane Music, publisher of Dreamworks, Paramount and Marvel, Elvis, Quincy Jones and the "Black Eyed Peas."  Hardback, 304 p.