Expanding stationary light in flight path, got bigger then waned and vanished

I'm watching plans land in distance from Red Rocks. One "plane" doesn't drop nor increase in altitude. It is very slowly getting brighter as well. I point it out to my wife and she sees the bright light but she was focused on the concert and not paying me much mind. The object appeared to stay in exact altitude over about 1-2min as other planes land and take off. It appeared to be coming towards red rocks but not changing altitude and moving slower than planes in area. At the very end the light got very bright, see picture. This caused be to finally believe what I was seeing and I pulled my phone out. 5-10 seconds after I take the picture the object gets very bright then starts to go all the way dim but brights back up for split second at very end then just collapsed into nothing, just disappeared right in front of me. I was not on drugs, don't drink alcohol. I'm also attaching picture about 1hr before the sighting when a full rainbow came up behind the stage with secondary rainbow developing to the left. Not sure if you see the two connected or not but both were first for me in my 44 years!! Crazy how it disappeared.