Comedians send up Christmas specials at their own peril. The genre is already self-parody, as can be proven with a quick YouTube glance at David Bowie's dueling duet with Bing Crosby in 1977 or Kathie Lee Gifford's 1995 hip-hop rendition of "The Night Before Christmas."

Stephen Colbert takes a whack at it with "A Colbert Christmas: The Greatest Gift of All" tonight at 10 on Comedy Central, and even he falls a little short. Colbert is delightful, a few of the song parodies are clever, but overall, the show is too long and more than a little strained, much like the holiday specials it mocks. Elvis Costello is one of the guests, and he is misused, forced into silly mock-skits that are no funnier than the cloying fluff they parody. He doesn't sing until the very end. When he does, alongside Colbert in a bittersweet carol called "There Are Much Worse Things to Believe In," it's not meant to be funny but it is quite wonderful.

The Christmas conceit puts Colbert in Andy Williams mode in a red turtleneck sweater and a white cable-knit cardigan in front of a fake roaring fire in a snow-bound cabin. Colbert stays in character as the kind of bombastic, self-centered host he plays on "The Colbert Report," and it might have been funnier to keep him in his natural habitat, the television studio.

Guests drop in and sing, and so does Colbert, not at all badly. The country singer Toby Keith performs a teasing tribute to Lee Greenwood's anthem "Proud to Be an American." ("There's a war on Christmas/It's under attack/ This year America is taking it back/ Separate church and state, that's what some lawyer said/ I say it's time to separate him from his head.")

The R&B singer John Legend makes fun of his own let's-have-sex style of torch song with an ode to nutmeg ("I'll sprinkle your Christmas cream/ With my spice supreme") and Jon Stewart, who can't really sing, does anyway, trying to persuade Colbert to switch over to Hanukkah, which he describes as "not my least unfavorite time of year." Colbert greets his former boss on Comedy Central by saying he didn't realize Stewart had his own cabin nearby. "It's half an hour earlier from here," Stewart replies pointedly. "You used to live there."

Stewart and Colbert are quite funny together, and there are other bright spots, but overall "A Colbert Christmas" isn't so different from an ordinary Christmas special. As Tom Lehrer once put it, "Kill the turkeys, ducks and chickens/ Mix the punch, drag out the Dickens/ Even though the prospect sickens/ Brother, here we go again."