Colo. Rev. Stat. § 43-4-512
No action by an authority to establish or increase any annual motor vehicle registration fee authorized by this part 5 shall take effect unless first submitted to a vote of the registered electors of that portion of the combination in which the fee is proposed to be collected at a general election, or a special election to be held on the first Tuesday after the first Monday in February, May, October, or December. Such action shall not take effect unless a majority of the registered electors voting thereon at the election vote in favor thereof. The election shall be conducted in substantially the same manner as county elections, and the county clerk and recorder of each county in which the election is conducted shall assist the authority in conducting the election. The authority shall pay the costs incurred by each county in conducting such an election. No moneys of the authority may be used to urge or oppose passage of an election to establish or increase any annual motor vehicle registration fee authorized by this part 5.
C.R.S. § 43-4-512