Colorado became the 38th US state on 1 August 1876, 100 years after the birth of the United States as a nation. It wasn't until 1911, however, 35 years later, that Colorado's state flag was officially adopted by the state legislature. The display of the flag after its adoption resulted in various shades to the background colors and designs of the central red “C” symbol surrounding a gold disk that was used. This resulted in the state General Assembly enacting a rule in 1929 that the blue and red colors of Colorado's state flag would be the same shade as those used in the US national flag. A further addition to the rules for Colorado's state flag design was enacted in 1964, when the yellow disk within the central “C” symbol was decreed to be the same diameter as the horizontal white stripe that runs down its center, which is bordered by equal blue stripes, both on the top and bottom of the flag.
The colors that Colorado's state flag use are themselves symbolic. The gold or yellow disk at its center is meant to represent the fact that Colorado has an abundance of sunshine, and suggestions are that it also represents the gold rush period in Denver, Colorado, during the mid-1800s. The central white strip represents snow-capped mountains in Colorado, such as the Rocky Mountain chain, while the blue border stripes flag reflect the state's climate, which is often one of storm-free and brisk blue skies. The red color of the central “C” symbol was also chosen to reflect the fact that Colorado has a lot of soil with a red color to it, either from clay or ferrous oxide content.
The “C” also has its own level of state connotations. It is meant to stand for the state flower, the columbine, the state name of Colorado, and the fact that it became a state on the centennial date of the birth of the United States as a nation. Colorado's state flag is also added to road signs within the state, which is not a common practice throughout US states in general. This may in part be due to the fact that many state flags in the US do not have a letter signifying the name of the state on them.
Colorado has a history of being under the authority of a diverse group of flags before the official adoption of its own. Francisco Vasquez de Coronado, the famous Spanish conquistador, made an expedition into an area including the state of Colorado in 1540 to 1542. Spain's claims to large areas of the New World at this time put the area under the rule of the Spanish flag. This authority changed hands to that of the French in the late 1600s, when the French explorer Robert de LaSalle claimed the entire Mississippi river basin that he visited in the name of the French King Louis XVI.
England then dominated land all the way west to the Pacific ocean into the 18th century, claiming Colorado as its own. The area subsequently flew under the flags of Mexico and the Republic of Texas, with the US officially buying the land in the Louisiana Purchase in 1803. Colorado then flew the flag of the District of Louisiana until it was given status as the Colorado territory in 1861.