Exhibit I: plain Emacs.

Exhibit II: Emacs under tmux.

The shades of colours are different, and importantly, the background colour differentiation is nil (e.g. look at the top menu). Anyone run into this?
I'm running tmux as tmux -2, $TERM in tmux is screen-256color, I'm using color-theme-solarized dark in Emacs, and Solarized for iTerm2 … a bit baffled!