Around 10:15 PM on the evening of the 4th, I walked outside to have a cigarette. We had stayed in this year rather than fight the crowds and had just put the kids to bed. It was overcast and foggy that night, so I stepped outside and happened to look to the northeast toward Thornton (I live in south-central Denver) and thought, "Boy, that's an odd color for a helicopter running light." I saw a solid, stationary blue-green light about 30 degrees above the horizon below the cloud cover. It was not strobing or flickering like a landing or running light from a helicopter or airplane, nor was there any sound coming from the object I could tell. I estimated it was around 3 to 5 miles from me, so I found that odd as even on a night where fireworks are going off I should have been able to hear something, especially considering it was below the cloud cover.As I watched, the light faded, slowly at first but then picking up in speed until it went out entirely. At that point I figured it was probably just a very bright flare or firework that got hung in a thermal or something, and was about to turn around and go back inside when it reappeared in the same position. However, it had changed color from bluish-green to bright red. So bright it almost hurt to look at. It then started to slowly move horizontally in the sky to my position, and that's when I called my wife outside to look, as well. It did this another two or three times, fading out and then coming back alternating between blue-green and red, all the while either remaining absolutely stationary or tracking a few degrees horizontally, for about a minute. Then, it dimmed somewhat and shot off to the North in the general direction of Greeley where I lost sight of it behind the neighbor's trees.I have no idea what that object was, but I do believe there was an object emitting that light. When it dimmed, I could make out a faint outline of...something. There was a physical object behind this. What it was, I can't say. But I can most certainly tell you what it was not: It was not a helicopter; there was no noise nor did it move or accelerate in any manner a helicopter could. When it took off I would estimate it went from stationary to about 250-300 knots or faster in a matter of a few seconds. It was not an airplane; airplanes cannot hang in the sky like that and, besides, I would have heard either a turboprop or turbofan engine. I grew up just up the road from Davis Monthan AFB, and have seen my share of both civilian and military aircraft. It was not a jetliner, nor was it a C-130, C-5, A-10, F-15, F-16, or F-18. We get a lot of civilian traffic coming over our house from both DIA and smaller aircraft from Centennial airport, so if it was a plane from either of those, or from Buckley AFB, I would have recognized it by sound. It was not fireworks. Unless, of course, someone has invented a firework capable of holding position, changing colors multiple times slowly, and able to propel itself along faster than most WWII fighter planes could. It was not a flare. See above. It was not jumpers parachuting into any of the fireworks shows around town with sparklers on their suits. At 10:15, all of the major shows had already ended. Additionally, I've seen them jump into shows before. See flares above. As I said, my wife saw this as well, but chalked it up to being a helicopter or drone. At least I know I'm not crazy, however. I did give a drone some thought, as an aside, but discarded it for the above reasons regarding traditional aircraft. It was, for all intents and purposes, a classic UFO.