tmux 2.0 on OSX: ~/.tmux.conf doesn't work

For some reason tmux didn't reload the ~/.tmux.conf when doing just exit and tmux again. So I addressed this issue with sudo kill $(pidof tmux). After starting new tmux session all worked properly

You can reload your config with tmux command:

:source-file ~/.tmux.conf

To access tmux command line type Ctrl + b (or whatever your prefix is) followed by : .

More details could be found here.