According to the Colorado Driver Handbook, which I just downloaded from the DMV website for confirmation, section 10.1a, if a traffic signal is malfunctioning or not operating, the intersection should be treated as a four-way stop. If the lights are on but flashing yellow, it is a warning of hazard, to slow and proceed with caution (but not "treat as a four-way stop").
For some reason, people in Colorado don't seem to understand these. When they're not completely ignoring them, they get these rules completely backwards.
Last week, I was driving home in the middle of the day to shuttle my wife to the auto shop, as we were down to one car while the minivan was having some maintenance (an $800 repair of the climate control system — ouch), when I noticed a stoplight was completely out. The road I was on was a six-lane divided road, and the intersection was with a small, two-lane road. A pickup was waiting on the cross street.
I slowed to a stop. A truck in the lane next to me blowed through the intersection, and I honked at him — which earned me an irritated honk from the truck behind me. I waited patiently as three more cars blew through the opposite direction before the pickup finally got his turn to go through the intersection, which, as you'll note in my first paragraph above, is legally a four-way stop at this point.
The next street light is also in a "non-standard" mode, but this one is blinking yellow. (The street I'm on has reduced to a two-lane road by this point.) Wouldn't you know it, traffic coming the other way is actually stopping at this blinking yellow light. I slow a bit, to make sure the car waiting on the cross street at his blinking red light doesn't try to pull out in front of me, and cautiously proceed through the intersection.
After I pick up my wife, we head back on the same road. I notice people are now treating the dead light like a four-way stop, but I believe this is due to the police car that has stopped beside the intersection, as a cop is donning an orange vest to direct traffic.