The 13-cent Colorado State Flag stamp (Scott 1670) features an image of the state flag adopted on June 5, 1911. The 1911 legislation that adopted the flag did not stipulate the precise hues of red and blue to be used, and so on February 28, 1929, the General Assembly stipulated that the colors be the same as the colors on the U.S. flag. Controversy arose over the size of the letter 'C,' and on March 31, 1964, the General Assembly further modified the 1911 legislation by revising the distance from the staff for the letter 'C' and its diameter.
Three alternate stripes comprise the flag's field—the two outer stripes are blue and the middle stripe is white. The center of the red letter 'C' is filled with the color gold.
The Colorado state flag's colors represent the state's environmental qualities. The gold represents abundant sunshine; blue symbolizes Colorado's clear blue skies; white represents the state's snow capped mountains; and red represents the color of much of the state's soil.
Scott 2005 Specialized Catalogue of U.S. Stamps and Covers
SHG Resources (http://www.shgresources.com/co/symbols/flag/)