Colorado has something in it's constitution called "Home Rule" for municipalities (as I understand it, some other states do as well). With regards to this conversation we had last month, Denver fought the "Firearms Preemption Law" passed by the state, using Denver's "Home Rule" status. Essentially as I understand it, "Home Rule" allows some autonomy to a municipality and also, I believe, allows some municipal ordinances to carry force of law (I'm not a lawyer, so I'm not 100% on this part).
To Alxone,
I wouldn't Open Carry in Denver. Unless you are trying to make a political statement (and that may not be that good of a reason), there's no good reason to. Tactically it's unsafe and it's illegal. If you don't have a CCW, go fulfill the requirements and get one. It should cost you around $300 for training and the application fee and take around 90 days to get the permit once you submit your application. You will be much better off Conceal Carrying than Open Carrying.