Verna Keays of Casper, Wyoming, designed the Wyoming state flag, adopted on January 31, 1917. The 13-cent Wyoming State Flag issue (Scott 1676) features an image of that flag.
A bison, the Wyoming state mammal, is centered on a blue field bordered in white and red. The state seal is branded on the bison. The woman represents the state motto—"Equal Rights"—and the two men represent cattle ranchers and miners. The words "Livestock," "Mines," "Grains," and "Oil" represent Wyoming's wealth. The eagle and shield signify support for the United States. The dates establish the years Wyoming was organized as a territory of the U.S. (1869) and its statehood (1890).
The colors of the state flag are the same as those of the U.S. flag. The red border represents Native Americans, the original settlers, and the blood of the pioneers who gave their lives claiming the soil; white is the emblem of purity and uprightness; and, blue, the color of the sky and mountains, is symbolic of fidelity, justice, and virility.
Scott 2005 Specialized Catalogue of U.S. Stamps and Covers
SHG Resources (http://www.shgresources.com/wy/symbols/flag/)