I think it's a female or juvenile. It looks a little like a photo of a bronzed cowbird, but not sure they're in Colorado. I'm not terribly good at this, so don't trust me! ;-)
This has really been bugging me. I have to say that I think it's a juvenile starling. The shape seems right. Perhaps the black at the head is just there because he (or she) is starting to change colors.
Thanks for the comments.
The bird hasn't been back...darn it. I did crop the pictures and attached them. Hope that helps.
I don't think he is a juvenile starling from the pictures I see on the web. Shape is good but not as much color and beak is black not yellow. Please send the link again Gary. We can't get it to work.
Take care.
Tom