Perhaps you thought deep maroon radicchio was an exotic enough looking salad green. Now Bella Vita Produce is importing two Italian "designer" radicchios: Castelfranco, at first taste mildly sweet, then delicately sharp; and Late Red di Treviso, with long, skinny, purple-tipped white ribs. Both are terrific in salads, or even just chopped and tossed with olive oil and salt; the sturdier Treviso can also be grilled ($14 to $20 per lb; 800-491-VITA). American relations of both are showing up at farmers' markets and specialty food shops ($6 per lb).