title: Vim 256 colour strange behaviour with tmux
body: <p>Just an interesting little problem I've got going on with terminals. I'm using vim inside of gnome-terminal. I like to have 256 colours so I don't have to use gVIM. </p>
  
  <p>My relevant .zshrc settings are:</p>
  
  <pre><code>export TERM=xterm-256color
  </code></pre>
  
  <p>My relevant .vimrc settings are:</p>
  
  <pre><code>if $COLORTERM == 'gnome-terminal'
    set t_Co=256
  endif
  </code></pre>
  
  <p>You'll notice from this showterm what the problem is:
  <a href="http://showterm.io/06460aeb043cac4bd0256" rel="nofollow">http://showterm.io/06460aeb043cac4bd0256</a></p>
  
  <p>I'm getting a weird background colour with the tmux vim. Any help on this would be great.</p>