High Quality Content by WIKIPEDIA articles! Since 1913, the U.S. state of Colorado has issued license plates for vehicles registered there.In 1956, the U.S. states and Canadian provinces came to an agreement with the Automobile Manufacturers Association that fixed the size for all their passenger vehicle plates at six inches in height by twelve inches in width, with standardized mounting holes. The 1955 (dated 1956) issue was the first Colorado license plate that complied with these standards. However, the 1954 (dated 1955) issue was six inches in height by twelve inches in width, although the mounting holes were not in these standardized positions.