TheWrap: CBS brought out its biggest gun at the network’s upfront presentation at New York’s famed Carnegie Hall on Wednesday: Stephen Colbert, who’s poised to take over “The Late Show” after David Letterman retires. The former “Colbert Report” host cracked up advertisers as he joked about ditching his conservative persona. Colbert also took a shot at Fox boss Rupert Murdoch, telling the assembled advertisers that they “want young eyeballs, and not just the ones Rupert Murdoch buys on the black market.”