Whether or not you believe in aliens, there is no denying that every now and then there are odd "unidentified flying objects" in the sky. Remember, that's what UFO stands for, after all. And in 2019 there were quite a few UFO's reported in Colorado.
The National UFO Reporting Center, which tracks calls and messages from people around the U.S. and Canada about strange sightings in the sky, reported that it received 5,971 sightings in 2019, a jump from 3,395 in 2018. That includes over 140 in Colorado alone.
If you need to waste a little time on the internet, you can read about each of them here.