I have to say that the tmux-users mailing list in general, and Nicholas Marriott in particular, are really nice and friendly.
I had a feature request (256 colors in fbterm so you can get 256 color tmux/vim without x), quickly got patch code, got support (I had never used patch before and didn't tell it to ignore whitespace) and when it worked, was told it would be in 1.9, and there it is. :-)
Just spent half an hour trying to figure out why 256 color mode stopped working in Vim.
I'm blaming you =P
In all seriousness actually trying to get 256 colour mode auto detecting and working reliability across different xterms, tmux/screen, ssh and so on, without some hack that forces the 256 on even when it's not supported seems impossible :/
I added the following to my zshrc, which seems to have helped. Why don't these terminals report 256 color mode by default?
if [ "$COLORTERM" == "yes" -a "$TERM" == "xterm" ]; then
export TERM=xterm-256color
fi
The escape sequences to set 256 colors were previously hardcoded into tmux, instead of detected from terminfo. That works fine, until you use a program that uses different escape sequences.
I suspect terminals don't set 256 colors by default for backward compatibility reasons. tmux itself didn't assume, you needed something in your config file or a command line option. Now though, I believe it can detect it based on your term.
I had a feature request (256 colors in fbterm so you can get 256 color tmux/vim without x), quickly got patch code, got support (I had never used patch before and didn't tell it to ignore whitespace) and when it worked, was told it would be in 1.9, and there it is. :-)