New York (AFP) – Andy Warhol’s iconic sage-blue background portrait of Marilyn Monroe is tipped to sell for a record-breaking $200 million at auction in the spring, Christie’s announced Monday. The auction house said it expects Warhol’s 1964 “Shot Sage Blue Marilyn” to become the most expensive 20th century artwork when it goes under the hammer in New York in May. The silk-screen work is part of a group of Warhol portraits of Monroe that became known as the “Shot” series after a visitor to his Manhattan studio, known as “The Factory,” apparently fired a gun at them. In a statement, Christie’s …