Colo. Rev. Stat. § 7-80-501
The contribution of a member may be in cash, property, or services rendered or a promissory note or other obligation to contribute cash or property or to perform services. A person may be admitted to a limited liability company as a member of the limited liability company and may receive a membership interest in the limited liability company without making a contribution or being obligated to make a contribution to the limited liability company. Unless otherwise provided in the operating agreement, a person may be admitted to a limited liability company as a member of the limited liability company without acquiring a membership interest in the limited liability company. Unless otherwise provided in the operating agreement, a person may be admitted as the sole member of a limited liability company without making a contribution or being obligated to make a contribution to the limited liability company or without acquiring a membership interest in the limited liability company.
C.R.S. § 7-80-501