The U.S. state of Colorado first required its residents to register their motor vehicles and display license plates in 1913.
The basic design of Colorado's license plate, a range of mountains against a white or green background, has been in use since 1960 (except for 1973 and 1975–76).
In 1956, the United States, Canada, and Mexico came to an agreement with the American Association of Motor Vehicle Administrators, the Automobile Manufacturers Association and the National Safety Council that standardized the size for license plates for vehicles (except those for motorcycles) at 6 inches (15 cm) in height by 12 inches (30 cm) in width, with standardized mounting holes.
Motorcycle plates continued to use two-letter codes (some of which were reassigned to other counties), with revised formats featuring three and later four digits between the letters (e.g. A123A and A1234A in Denver).
When the current passenger baseplate was introduced in 2000, the state also simplified its non-passenger and specialty plates, issuing them in the same serial format (originally 123-ABC) and with similar graphic elements.