C.R.S. 10-4-609(1)(c): 

The coverage described in paragraph (1) of this subsection (1) (UM-UIM) shall be in addition to any legal liability coverage and shall cover the difference, if any, between the amount of the limits of any legal liability coverage and the amount of the damages sustained, excluding exemplary damages, up to the maximum amount of the coverage obtained pursuant to this section.  A single policy or endorsement for uninsured or UIM coverage issued for a single premium covering multiple vehicles may be limited to applying once per accident.  The amount of the coverage available pursuant to this section shall not be reduced by a set off from any other coverage, including, but not limited to, legal liability insurance, medical payments coverage, health insurance, or other uninsured or underinsured motor vehicle insurance.

 (4) Uninsured motorist coverage shall include coverage for damages for bodily injury or death that an insured is legally entitled to collect from the owner or driver of an underinsured motor vehicle.  An underinsured motor vehicle is a land motor vehicle, the ownership, maintenance, or use of which is insured or bonded for bodily injury or death at the time of the accident.