Casey MacGill’s Blue 4 Trio performs music that swings. Nat “King” Cole Trio meets the Mills Brothers. Fats Waller meets Fats Domino. Slim Galliard meets Fred Astaire. It is music of many decades and no decade in particular, all happening at the same time, woven into a seamless, beautiful whole. At the core of this group’s sound are the band’s sometimes sweet, sometimes rough-hewn three-part harmony vocals and a piano-ukulele-bass-and-drums rhythm section that swings in a variety of textures.