Uma Thurman, Jesse L. Martin, and Jane Krakowski are going green — specifically, the shade of Kermit. The three actors have signed on to NBC’s holiday special Letters to Santa—A Muppets Christmas, which airs Dec. 17. (New York City mayor Michael Bloomberg will also make a cameo.) In the one-hour special, which features songs by Paul Williams (The Muppet Movie), Kermit, Miss Piggy, and other Muppet faves must deliver three letters to Santa Claus in time for Christmas. Previously announced cast members include Whoopi Goldberg, Richard Griffiths, Tony Sirico, and Steve Schirripa.