Colorado is a little bit interesting. The State of Colorado has specific legislation which prevents cities and counties from creating breed specific legislation.
However, some cities in Colorado have adopted "home rule" charters. Which basically state the the city acts as the basic governing body.
There 196 towns and 73 cities in Colorado, of which 61 cities and 35 towns are home rule municipalities. Source
You can read more about home rule charters here.
Sec. 8-67. - Pit bulls prohibited without breed-restricted permit.
(a)It shall be unlawful for any person to own or keep any pit bull within the city without first obtaining a breed-restricted permit satisfying the conditions set forth in this section. "Breed-restricted permit" under this section shall mean a permit granted by animal protection to owners or keepers of a pit bull in accordance with certain conditions.
Original ordnance has been removed Municipal Code book. However, there is no documentation noting the change in law.