To color code your opportunities in the list view based on the alert levels, click the ColorCode View.
If the Days in Stage field is displayed in the view, it will only colorize that field. Otherwise it will colorize the entire row.
If you wish to systematically colorizxe your view and not have to press the button each time, open the add-on and go to Options > Preferences, you'll see you have an option to always color code the list view.