Good question. IANAL, but here's how the law currently reads:
"Unless a specified exception applies, before any person who is not a licensed gun dealer transfers or attempts to transfer possession of a firearm, he or she shall:
Require that a background check be conducted of the prospective transferee; and Obtain approval of the transfer from the Colorado bureau of investigation (bureau) after a background check has been requested by a licensed gun dealer."
http://www.leg.state.co.us/clics/cli...229sstaapp.pdf