Does tmux support saving to a file the commands typed in "C-b :" mode ? I'd rather look through the ones I already typed than have to look each command up in the man page.
history-file option which does what you are looking for.
If not empty, a file to which tmux will write command prompt history on exit and load it from on start.
Add this to your
set -g history-file ~/.tmux_history
Note it was added in 2.1 version. if you have older version of tmux read http://unix.stackexchange.com/questions/26548/write-all-tmux-scrollback-to-a-file