Welcome to the forum, mitch77. Since you posed this question in the open-carry forum, I presume you are asking how many carry openly. Open carry is not prohibited here (outside of Denver), but very few do so. But you may really be asking about concealed carry, for which we do have some data.
According to the latest data (2009 Aug) located at
http://cbi.state.co.us/ic/Statistics/2009stats/August 2009 Firearm Stats.pdf , there have been 86,756 Colorado concealed-weapon permits issued since the inception of shall-issue in 2003.
The State Demography Office estimates the current population of Colorado to be 5,109,700, so the maximum possible rate of legal carry is about 1.7%. Of course the actual rate may be less because it's possible that some with permits don't carry. Also Colorado LEOs carry using their LEO credentials rather than concealed weapon permits.