C.R.S. § 38-36-103: When tax title may be registered.

No title derived through sale for any tax or assessment or special assessment shall be entitled to be registered unless it appears that the title of the applicant, or those through whom he claims title, has been adjudicated by a court of competent jurisdiction, and a decree of such court duly made and recorded decreeing the title of the applicant, or that the applicant or those through whom he claims title have been in the actual and undisputed possession of the land under such title at least seven years immediately prior to the application, and has paid all taxes and assessments legally levied thereon during said time; unless the same is vacant and unoccupied lands or lots, in which case, where title is derived through sale for any tax or assessments or special assessment for any such vacant and unoccupied lands or lots and the applicant, or those through whom he claims title, have paid all taxes and assessments legally levied thereon for eight successive years immediately prior to the application, in which case such lands and lots shall be entitled to be registered as other lands provided for by this section.