score:34
It's historical, dating from before the two colours represented different ranks instead of different branches of the army, as a cost-saving measure (essentially).
From Wikipedia:
The Army origin explains why the color silver outranks gold in Air Force officer insignia. In the early 19th century, Army infantry colonels wore gold eagles, while all other Army colonels wore silver eagles. When the Army later decided to adopt a single color of eagles for all colonels, that single color was silver, apparently because more silver eagles than gold eagles were already in use. Lieutenant colonels received silver oak leaves next, to match the silver eagles of full colonels. Majors were then given gold oak leaves to distinguish them from lieutenant colonels. Once the precedent of silver outranking gold was set, it was followed when gold bars were later created for second lieutenants, who had no grade-specific insignia until the early 20th century.
Update:
I found this complete History of U.S. Army Grade Insignia through 1866. I note that the early adoption of silver jewelry resulted in a high contrast when worn over gold epaulettes. Also, as late as 1866 Second Lieutenants wore no insignia jewel while First Lieutenants and Captains wore a silver jewel with high contrast against the gold braid. This is completely consistent with the note in Wikipedia that I quoted above.
Upvote:2
In the mid 60's I served in the Army Reserve. Military Army and Marine officer ranks were explained by an instructor as follows.
Symbols follow their appearance in nature. Going from low to high; silver is found at a higher elevation than gold, oak leaves (including other reasons) still higher, eagles still higher, and stars highest.
Sure hope this explanation has significance since I've been passing this on for some time.
Upvote:4
One after-the-fact explanation suggested by some NCOs is that the more-malleable gold suggests that the bearer is being "molded" for his or her responsibilities -- as a field officer (second lieutenant) or staff officer (major). However, this explanation may be more clever than correct, for while the insignia for second lieutenant and major are gold colored they are actually made of brass, and brass is a base metal while silver is a precious metal. The rank order thus does not actually conflict with heraldic tradition.
Source: US Military Rank Insignia
Upvote:5
There is a fine PDF booklet by Raymond Oliver, then curator of the Air Force museum at McClellan AFB in Sacramento, "Why is the Colonel Called "Kernal" which explains the origin of military ranks and their associated insignia.