Colo. Rev. Stat. § 24-51-1743
The election described in section 24-51-1742 shall become irrevocable upon the first payment thereunder of any benefits provided under sections 24-51-1736 to 24-51-1746 or under sections 24-51-1713 and 24-51-1714. If, subsequent to exercise of such election by the appropriate beneficiary or beneficiaries but prior to the first payment of benefits thereunder, such beneficiary or beneficiaries desire to revoke such earlier election, such person or persons shall be permitted to do so and shall thereupon be eligible to receive a refund paid under the terms and conditions set forth in section 24-51-1735, and such revoking beneficiary or beneficiaries shall thereafter have no rights to any benefits of any kind, incident to the death of such member, other than said refund. If the election has been made to receive benefits hereunder and there is only one beneficiary and such beneficiary shall die before any payment of such benefits is made, a refund of such deceased member's accumulated contributions, computed as of the date of death, shall be made to the estate of such deceased beneficiary. If there shall be more than one beneficiary but all of them shall have died before any payment of such benefits is made, such refund shall be made to the estate of the last survivor of said several beneficiaries.
C.R.S. § 24-51-1743