I've tried different themes in emacs (on mac with xterm set to 256) and everything works great except it's ignoring the theme's background color. Even if I add (set-background-color "red") for example to my .emacs file, it simply ignores this and uses the default terminal background of OS X.
I cannot replicate your problem. I am using Emacs 24.3.1 which you can get either from emacsformacosx.com or MacPorts. Running Emacs with
emacs -nw in Terminal.app (
M-x customize-theme I can select themes with colored backgrounds -- see attached image.
It may be that the OS X Emacs
/usr/bin/emacs, which is version 22.1.1 in Mavericks, does not support this, but Emacs 22 is ancient anyway.
So I suggest you install the current Emacs and try it out.