Colo. Rev. Stat. § 39-11-116
If a person bidding fails to pay the amount due, the treasurer may again offer the tax lien on such land for sale if the public auction has not closed, and, if it has closed, the treasurer may again advertise it specially in the same manner as in the original advertisement and for not less than one week, after which the treasurer may again offer and sell the tax liens on such lands or lots as provided in section 39-11-115; or at the treasurer's option, the treasurer may recover the amount bid by civil action brought in the name of the county in any court of competent jurisdiction. In a public auction conducted by means of the internet or other electronic medium, if a person bidding fails to pay the amount due, the treasurer may offer the tax lien, without additional advertisement, to another bidder, whether or not the public auction has closed; or at the treasurer's option, the treasurer may recover the amount bid by civil action brought in the name of the county in any court of competent jurisdiction. The treasurer may prohibit a person who fails to pay the amount due from bidding on sales under this article for up to five years.
C.R.S. § 39-11-116