Colorado Revised Statutes § 2-4-211 states:
The common law of England so far as the same is applicable and of a general nature...shall be considered as of full force until repealed by legislative authority.

In re Application of Knight, 537 P. 2d 1085 - Colo: Court of Appeals, 3rd Div. 1975 states:
"At common law, a person could adopt another name at will. Statutes setting forth procedures to be followed in changing a name merely provide an additional method for making the change. See 57 Am.Jur.2d Name §§ 10 and 11."

In re Marriage of Nguyen, 684 P. 2d 258 - Colo: Court of Appeals, 2nd Div. 1984 states:
The procedure for change of name set forth under §§ 13-15-101, et seq., C.R.S.1973, is in addition to, not in exclusion of, the common law method for change of name.

Hamman v. County Court, Jefferson County, 753 P. 2d 743 - Colo: Supreme Court 1988 states:
The court noted that the name change procedure found in section 13-15-101 "is in addition to, not in exclusion of, the common law method for change of name." Id. at 260.

Brown v. Cooke, Dist. Court, D. Colorado 2009 states:
Certain principles are not in material dispute in this action. The common law of many states, including Colorado, recognizes the ability of persons to change their name, in most instances, simply by making use of their newly-chosen name. In re Marriage of Nguyen, 684 P.2d 258, 260 (Colo. App. 1983) (acknowledging common-law right to change name); Eisenberg v. Strasser, 768 N.Y.S.2d 773, 776 (N.Y. Sup. Ct. 2003) (common-law change typically effected simply by use of new name); In re Arnett, 56 Cal.Rptr.3d 1, 3 n. 3 (Cal. App. 2007) (same). And, as Mr. Brown points out in his Objections, many courts have observed that the effect of a common-law name change is to make the chosen name "his legal name just as though given at birth," see e.g. Liebowitz, 49 F.Supp. at 954