Sean Carroll reports on what goes on before and after the actual taping, in Cosmic Variance:
We got picked up at our hotel in a car that brought us to the Colbert studio, and hustled inside under relatively high security — people whispering into lapel microphones that we had arrived and were headed to the green room. Very exciting. The green room was actually green, which is apparently unusual. I got pep talks from a couple of the staff people, who encouraged me to keep things as simple as possible. They made an interesting point about scientists: they make the perfect foils for Stephen’s character, since they actually rely on facts rather than opinions.
Stephen himself dropped by to say hi, and to explain the philosophy of his character — I suppose there still are people out there who could be guests on the show who haven’t ever actually watched it. Namely, he’s a complete idiot, and it’s my job to educate him. But it’s not my job to be funny — that’s his bailiwick. The guests are encouraged to be friendly and sincere, but not pretend to be comedians.
We got to sit in the audience as the early segments were taped, which were hilarious. I feel bad that my own interview is going to be the low point of the show, laughs-wise. But I went out on cue, and fortunately I wasn’t at all jittery — too much going on to have time to get nervous, I suppose.
I had some planned responses for what I thought were the most obvious questions. Of which, he asked zero. Right off the bat Colbert managed to catch me off guard by asking a much more subtle question than I had anticipated…
More, including video of the interview, here.