Colo. Rev. Stat. § 39-26-115
If any part of the deficiency is due to negligence or intentional disregard of authorized rules and regulations with knowledge thereof, but without intent to defraud, there shall be added ten percent of the total amount of the deficiency, and interest in such case shall be collected at the rate imposed under section 39-21-110.5, in addition to the interest provided by section 39-21-109, on the amount of such deficiency from the time the return was due, from the person required to file the return, which interest and addition shall become due and payable ten days after written notice and demand to him by the executive director of the department of revenue. If any part of the deficiency is due to fraud with the intent to evade the tax, then there shall be added one hundred percent of the total amount of the deficiency, and, in such case, the whole amount of the tax unpaid, including the additions, shall become due and payable ten days after written notice and demand by the executive director, and an additional three percent per month on said amount shall be added from the date the return was due until paid.
C.R.S. § 39-26-115