Colo. Rev. Stat. § 24-51-1722
In addition to the options provided in sections 24-51-1717 and 24-51-1721, any contributing member or affiliate member whose effective date of retirement is on or after December 31, 2004, may elect to receive a superannuation retirement allowance in accordance with any of the options provided in sections 24-51-1723 and 24-51-1724. Option A shall be deemed a basic option under this section, and the amount of the annual retirement allowance payable thereunder, as determined under the provisions of section 24-51-1715, shall be the amount that shall be duly adjusted in computing payments to be made under options P2 and P3. Prior to application for retirement, any such election may be changed or revoked, but when a member files application for retirement and elects an option, such option may not thereafter be changed or revoked except as provided in this part 17.
C.R.S. § 24-51-1722