NEW YORK — Bright color, sportswear shapes and a certain all-American nonchalance — the key elements were all in place as one of fashion’s most stylish men said farewell to his metier. Bill Blass showed his final ready-to-wear collection on Thursday, and one of its linchpins was the sporty evening separates he’d long ago made his own. Here, his cutout sweater and spangled skirt. For more on spring, see pages 6 to 10.