When I was brave enough to test outside of urxvt and iterm2/terminal.app, it seemed that terminal emulators are all over the place in terms of background color support in vim terminal mode.
You might have tried this already (and it might not actually be related to your issue), but there is a variable you stick in your vimrc (let g:solarized_termtrans=1) to force it to take the background of your terminal emulator (useful only if you are running with the solarized colors in terminal mode).
I should come up with a some recommendations on setting TERM to ensure proper colorscheme support, but that way lies madness (for me at least).
You might have tried this already (and it might not actually be related to your issue), but there is a variable you stick in your vimrc (let g:solarized_termtrans=1) to force it to take the background of your terminal emulator (useful only if you are running with the solarized colors in terminal mode).
I should come up with a some recommendations on setting TERM to ensure proper colorscheme support, but that way lies madness (for me at least).