Colorado common law marriage factors
        Cohabitation - even for one day
        Sexual intercourse
        Holding yourselves out as married to third persons
        Intent to be married at the present time
                Colorado common law marriage does not exist at present if you intend to become married in a future
                wedding ceremony
        Some married couples renew their vows in a subsequent ceremony - facts dictate        

Evidence of reputation and intent - what do lawyers look for?
        Filing joint federal or state tax income tax returns as husband and wife
        Joint debt - application as husband and wife or account name "John Jones & Susan Jones"
        Joint lease - application as husband and wife or lease held as "John Jones & Susan Jones"
        Joint ownership of assets as husband and wife or title held as "John Jones & Susan Jones"
        Real property deed, deed of trust or mortgage
        Motor vehicle titles
        Checking, savings, money market certificates, certificates of deposit
        Life insurance policies
        Last will and testament devising or bequeathing property to "my husband" or "my wife"
        Written communications - special occasion cards and letters to "spouse" or family members
        Holding yourselves out verbally to neighbors, family, friends or business associates as married
        Name change, whether by name change lawsuit or simply adopting usage of the surname
        Executed Colorado Dept. of Revenue, Div. of Motor Vehicles Affidavit of Common Law Marriage
                If the wife changes her driver's license, you each may have executed such a DMV affidavit
                Common Law Marriage - Colorado Department of Law - FAQ

The Colorado Supreme Court is always polite & formal in its language, but it could be summarized:

The marriage is as lawful as if you had become married before a minister, judge or magistrate.  Legal separation is another alternative.  If you have a child or children and neither common law marriage nor statutory marriage (judge or minister) apply, paternity is the proper remedy.

CRS 14-2-110. Prohibited marriages.
        (1) The following marriages are prohibited:
                (a) A marriage entered into prior to the dissolution of an earlier marriage of one of the parties, except a currently valid marriage between the parties;
                (b) A marriage between an ancestor and a descendant or between a brother and a sister, whether the relationship is by the half or the whole blood;
                (c) A marriage between an uncle and a niece or between an aunt and a nephew, whether the relationship is by the half or the whole blood, except as to marriages permitted by the established customs of aboriginal cultures.
        (2) Children born of a prohibited marriage are legitimate.

CRS 14-2-111. Putative spouse.
        Any person who has cohabited with another to whom he is not legally married in the good faith belief that he was married to that person is a putative spouse until knowledge of the fact that he is not legally married terminates his status and prevents acquisition of further rights. Children born of putative spouses are legitimate. A putative spouse acquires the rights conferred upon a legal spouse, including the right to maintenance following termination of his status, whether or not the marriage is prohibited under section 14-2-110, declared invalid, or otherwise terminated by court action. If there is a legal spouse or other putative spouses, rights acquired by a putative spouse do not supersede the rights of the legal spouse or those acquired by other putative spouses, but the court shall apportion property, maintenance, and support rights among the claimants as appropriate in the circumstances and in the interests of justice.