In uncertain times, people often seek comfort in the familiar, and what’s more familiar in fashion than Isaac Mizrahi’s optimism? That upbeat sensibility was in full force at his Thursday showing, which marshaled all his signatures into a terrific, back-to-his-roots sportswear collection: There was fabulous color, volume and every bit of his wit and spunk. Trademarks were made wholly current, as with great plaid sweaters and picnic blankets folded into skirts; staples like crisp blouses and long cardis were shot with yellow, green and hot pink. Mizrahi also sent forth a fresh take on business attire: a purple wool dress with brass buttons and matching boatnecked peacoat. Sure, some of these were whimsical clothes (consider the name of one look, a striped sweater and cherry-red jacket topped off with a handbag as hat: “Xanaxer”) but superpolished, too. Case in point: beautifully slinky beaded and velvet gowns, some worked with a delicate cherry blossom motif, and an array of smart coats, from a navy duster to a cropped olive-green leather number. Much was cleverly constructed — the cerise pleated silk dress and series of high-waisted, wide-legged trousers, for instance. But at heart these chic and accessible day clothes felt just right for the kind of woman who wants more than a fleet of pantsuits to fill her closet.