Key display/indication on alarm_regenerate to show that alert-checkers are useful

It would be really useful (for me) to have a key at the top of the screen for the box colours encompassing rebuilt alert-checkers on /alert_regenerate/action=update/.

I recently added my first alert-checker and after rebuilding saw that it had a blue box around it. Knowing the difference between a blue box (not actually checking anything, therefore alert-checker is useless?) and a green box (actually checking something?) would have been useful.