Restore Tmux notifier options; add option to turn off coloring

I was looking to customize the tmux notifier, but as best I can tell, it's been ignoring options since around the notifier refactor: https://github.com/jamesdabbs/guard/commit/53d91e0ed944ac5c4942170850190187b2e14989.

This should fix the option setting, along with adding an option to disable the color highlighting (since, in my case, I only want to display a message and not permanently change the background).