MORRISON, Colo. — Surrounded by the awe-inspiring geological formations that cradle Red Rocks Amphitheater here, Jemaine Clement and Bret McKenzie could not help but contemplate the passage of time.

On a cool July evening, these two comedians and musicians from New Zealand, who perform together as Flight of the Conchords, told more than 9,000 gathered fans that they were sorry for having grown older since their last tour of the United States three years ago.

As they age, Mr. Clement said, “It ultimately reminds you of your mortality, and for that, we apologize.”

Their advancing years are showing, too. “In that time,” Mr. McKenzie said, “we’ve come to like jazz music.”

For the 18 years that this band has existed, Flight of the Conchords has been distinguished by its subtlety: songs, jokes and stage banter so understated, you could be forgiven for not realizing when the two men performing them are joking.

“There’s a very blurred line between the material and us just talking about things,” Mr. McKenzie, 40, said earlier that afternoon as he sat beside Mr. Clement, 42, on a dressing-room couch.