Seems to me some bug was recently introduced related to theme colours. I noticed that on the current head themes like zenburn (https://github.com/bbatsov/zenburn-emacs) load with several errors - Unable to load color "unspecified-fg" and some faces in the theme are rendered with a black foreground (I guess those that generate the error).

As the theme looks good on Emacs 24.3 and nothing is apparently wrong with the colours Emacs head deems problematic, I'm fairly certain this is some bug/regression. Any ideas what change might be the cause of that problem?