It looks like the true color ticket on tmux was closed out: http://sourceforge.net/p/tmux/tickets/140/

I was applying this patch to 1.9 on my machine and it worked well: https://gist.github.com/JohnMorales/0579990993f6dec19e83

Haven't had a chance to see if the same diff can be applied to 2.0 yet.

I tried the same patch on 1.9a but couldn't get it to work (tmux built fine but no dice with 24 bit colours). Very curious to hear if it works with 2.0.

a couple of people have asked me about how true colour should look but none have sent code so far, it's not a very interesting feature to me so it'll need someone who cares about it to do it