I'm convinced the selection of branch color in the 19th century was based on the availability/low price of fabric and thread at the time of uniform change. Though now graved in stone, there was no hoary tradition involved at the time of their selection.
Regarding Will Gorenfeld's comments on rifles, many of our military traditions are British and they did use green to uniform their riflemen. The U.S. rifle regiments raised in the War of 1812 wore green pom-poms and green chords on their shakos. The Regiment of Mounted Rifles wore green insignia 1858-1861 according to plates in the collection of work by H. A. Ogden. We probably copied them, but I bet the Brits chose green for availability/price.
Not related to branch color, another Brit tradition we borrowed was calling riflemen "chosen men." Both Lewis and Clark served in a Chosen Rifle Company.
James B. Ronan II
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