Colo. Rev. Stat. § 24-51-1717
Option A is a single life annuity, which is defined as a specified sum of money payable monthly to an annuitant from the time of retirement until the death of said annuitant, without refund of any kind to the estate of the deceased annuitant or anyone claiming by or through the annuitant. The monthly retirement allowance under option A shall be calculated in accordance with the provisions of section 24-51-1715. For retirements having effective dates on or after December 31, 2004, option A shall be revised to provide that if, upon the death of the annuitant, the total amount of retirement allowance that has been paid to the annuitant does not exceed the amount of the member's accumulated contributions, then the difference between said accumulated contributions and the total amount of retirement allowance paid to such annuitant shall be paid to the named beneficiary of the annuitant or, if no named beneficiary exists, to the estate of the annuitant. The monthly retirement allowance under the revised option shall be calculated in accordance with the provisions of section 24-51-1715.
C.R.S. § 24-51-1717