Colorado Department of Revenue - Register your 50cc and under low-power scooter with the Colorado Dept of Revenue. The form can be mailed in or walk-ins can be done at the Lakewood Office. The sticker is valid for 3 years and costs $5.85. Read more about low-power scooter regulations at http://www.colorado.gov/cs/Satellite/Revenue-MV/RMV/1209847483655
Colorado Department of Motor Vehicles - Register your over 50cc scooter as a motorcycle with the Colorado Dept of Motor Vehicles. Emissions testing is not required for motorcycles along the Front Range. http://www.colorado.gov/cs/Satellite/Revenue-MV/RMV/1177024843137
Local government regulations can not change the state registration requirements for scooters.
How to get a Motorcycle Endorsement on your Colorado driver's license - http://www.colorado.gov/cs/Satellite/Revenue-MV/RMV/1190796317325