I can't seem to reproduce the problem here, if I use /color treebar N where N is a number from 0 to 15 the treebar background is updated immediately with the selected color. The same happens when modifying the treebar text color. Are you sure you are using the correct parameters, /color treebar N and /color "treebar text" N.
Other IRC clients don't support it, and messages would look awful to those.
Yeah it's a bit of a pain that other things hold mIRC back (and vice versa if other client authors have considered extending them) but IRC is about communication, so it wouldn't be a wise idea to start adding unsupported jargon to messages :tongue: