Officiants: Couples themselves may solemnize their own marriage (C.R.S 14-2-109). They must apply for paper work from the County Courthouse in order to do this. However, friends or relatives can not solemnize their marriage. Out-of-state Clergy need not be registered in Colorado.

Solemnizing a Marriage: Couples themselves may solemnize their own marriage (perform one's own marriage ceremony). According to Colorado Revised Statute 14-2-109, a marriage may be solemnized by a judge of a court; by a court magistrate; by a retired judge of the court; by a public official whose powers include solemnization of marriages; by Indian tribe officials; by clergy; by the parties to the marriage. If you wish to solemnize your own marriage, you will be responsible for acquiring, completing and returning

taken from:
http://usmarriagelaws.com/search/united_states/colorado/index.shtml

HTH!