“ Late Show ” host Stephen Colbert on Wednesday mocked Melania Trump for showing off her “signature pep” in a moody clip showcasing this year’s White House Christmas decorations. In a video backed by a mellow piano instrumental, the first lady is seen strolling past several Christmas trees that are wrapped in white lights before taking a closer look at a white ornament. “That is so sad. They didn’t even play a Christmas carol; they played the before-music from an anti-depressant commercial,”