Colorado's idling laws, as it pertains to all vehicles, with variations, below 15 deg. and above 80 deg. the state cannot prohibit idling on public property under those conditions. On private property is a different story, if someone complains, they can enforce them. However, each city has their own rules on this. Boulder and Aspen are draconian, I know of guys getting cited in Boulder for idling their semi while delivering new cars to the dealer, they have to keep their electric hydraulic pumps running somehow, cop said it didn't matter. Aspen prohibits idling unless below 0. Denver is kinda vague on it, if it's in a residential area, it becomes more about noise (diesel or loud exhaust), puffing if the vehicle is unattended (all).
In '08 when Denver hosted the DNC, the semi's delivering to Mile Hi were not allowed to idle while sitting in the queue, sometimes for up to 8 hrs, in 90 deg. temps. The enforcement officer, drove around in a police car, with the a/c on the entire time. The press tents, DNC operations tents and city operations tents used giant diesel generators shipped in on trailer chassis that smoked like a freight train and burn 10 gal of diesel per hour to provide power and operate the a/c units. They also used trash trucks filled with sand to block the highway ramps, those trucks sat and idled for 3 straight days, they actually delivered diesel and nat. gas to them, the drivers were allowed to sleep in the cabs.