One stop shopping for Colorado Purchase Laws

[baglock1]

In the case of a FTF sale, unless they're uber paranoid, your ID (sometimes your orders) and this should suffice:

Q: What constitutes residency in a State?
The State of residence is the State in which an individual is present; the individual also must have an intention of making a home in that State. A member of the Armed Forces on active duty is a resident of the State in which his or her permanent duty station is located. If a member of the Armed Forces maintains a home in one State and the member’s permanent duty station is in a nearby State to which he or she commutes each day, then the member has two States of residence and may purchase a firearm in either the State where the duty station is located or the State where the home is maintained. An alien who is legally in the United States is considered to be a resident of a State only if the alien is residing in that State and has resided in that State continuously for a period of at least 90 days prior to the date of sale of the firearm. See also Item 5, “Sales to Aliens in the United States,” in the General Information section of this publication.

[18 U.S.C. 921(b), 922(a) (3), and 922(b)(3), 27 CFR 478.11]

From here:
http://www.atf.gov/content/firearms-...censed-persons