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: 8d350744acd6e66be2744d5c57f93ed55b50019e.

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).