2 Answers

This was from another site that I found. As a former Air Force Historian, it looks right to me.

From 1872 the majors received oak leaves in gold to distinguish them from the silver of lieutenant colonels and the bars of both captains and lieutenants became silver. In a similar fashion, 1917 saw the introduction of a single gold bar for second lieutenants. These changes created the curious situation (in terms of heraldic tradition) of silver outranking gold. 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.

Link that discribes more of a real reason:
http://www.tioh.hqda.pentagon.mil/ROTCMi…

SSG Schramm
OIF 2003
US Army 15 years

Thank you bluedeath. I believe you to be right on!