Colorado Revised Statutes Title 14. Domestic Matters § 14-2-110. Prohibited marriages

(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;

(a.5) A marriage entered into prior to the dissolution of an earlier civil union of one of the parties, except a currently valid civil union between the same two 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.