Shoot, I've just updated my emacs and and I guess I can no longer set
frame-local color themes, a it says in NEWS:

** Some obsolete functions, variables, and faces have been removed:
*** make-variable-frame-local.  Variables cannot be frame-local any more.

Does anyone else rely on multiple color themes for visually distinguishing
frames or buffers? Do you have suggestions for how to do that now that this
deprecated function has been removed (sniff)?