CO Rev. Stat §10-16-106.5(5)(a)

A carrier that fails to pay, deny, or settle a clean claim in accordance with paragraph (a) of subsection (4) of this section or take other required action within the time periods set forth in paragraph (b) of subsection (4) of this section shall be liable for the covered benefit and, in addition, shall pay to the insured or health care provider, with proper assignment, interest at the rate of ten percent annually on the total amount ultimately allowed on the claim, accruing from the date payment was due pursuant to subsection (4) of this section.