Colo. Rev. Stat. § 24-91-105
The contractor under any contract exceeding one hundred fifty thousand dollars made or awarded by any public entity, pursuant to which sums are withheld to assure satisfactory performance of the contract, may withdraw the whole or any portion of the said sums withheld if the contractor deposits acceptable securities with the public entity. The contractor shall take such actions as the public entity may require to transfer the securities or a limited interest in the securities, including a security interest, and to authorize the public entity to negotiate the acceptable securities and to receive the payments due the public entity pursuant to law or the terms of the contract, and, to the extent there are excess funds resulting from said negotiation, the balance shall be returned to the contractor. Such acceptable securities so deposited at all times shall have a market value at least equal in value to the amount so withdrawn. If at any time a public entity determines that the market value of the acceptable securities theretofore deposited has fallen below the amount so withdrawn, the public entity shall give notice thereof to the contractor, who forthwith shall deposit additional acceptable securities in an amount sufficient to reestablish a total deposit of securities equal in value to the amount so withdrawn.
C.R.S. § 24-91-105