Captain Bishop,
I guess TR was a more than just a bit of a "free spirit," since the M1898 Officer Eagles were supposed to be on the collar for those Colonel or higher in place of the USV. And I would still state TR's uniform trim is, in fact, Cavalry yellow, since in the latest pic you have, he is still wearing the 1st Cavalry insignia, hence the photographic emulsions will show yellow as black...