Colo. Rev. Stat. § 40-3.5-102
The power and authority is hereby vested in the governing body of each municipal utility and it is hereby made the duty of each such governing body to adopt all necessary rates, charges, and regulations to govern and regulate all rates, charges, and tariffs of its municipal utility within its authorized electric and natural gas service areas which lie outside the jurisdictional limits of the municipality. No rate, charge, tariff, or voluntary plan approved pursuant to section 40-2-122 shall unjustly discriminate between or among those customers or recipients of any commodity, service, or product of the municipal utility within the authorized service area. In the event that any rate, charge, tariff, or voluntary plan established within the authorized service area which lies outside the jurisdictional limits of the municipality varies from the rate, charge, tariff, or voluntary plan established for the same class of customers or recipients of any such service within the authorized service area which lies inside the jurisdictional limits of the municipality, such rate, charge, tariff, or voluntary plan shall not become effective until reviewed and approved by the commission. Such review and approval shall be in accordance with the provisions of article 3 of this title; except that in no event shall the commission modify or establish such rate, charge, or tariff to an amount lower than that established by the municipality, or approve a voluntary plan that differs from the voluntary plan, for the same class of customers or recipients of any utility service within the authorized service area which lies inside the jurisdictional limits of the municipality.
C.R.S. § 40-3.5-102