Color coding the situation

This Jeff Cooper article covers the whole premise.

Rico says it's important stuff, so practice. It could save your life, or that of someone you love.

White - Relaxed, unaware, and unprepared. If attacked in this state the only thing that may save you is the inadequacy and ineptitude of your attacker. When confronted by something nasty your reaction will probably be, "Oh my God! This can't be happening to me."
Yellow - Relaxed alertness. No specific threat situation. Your mindset is that "today could be the day I may have to defend myself." There is no specific threat but you are aware that the world is an unfriendly place and that you are prepared to do something if necessary. You use your eyes and ears, and your carriage says "I am alert." You don't have to be armed in this state but if you are armed you must be in yellow. When confronted by something nasty your reaction will probably be, "I thought this might happen some day." You can live in this state indefinitely.
Orange - Specific alert. Something not quite right has gotten your attention and you shift your primary focus to that thing. Something is "wrong" with a person or object. Something may happen. Your mindset is that "I may have to shoot that person." Your pistol is usually holstered in this state. You can maintain this state for several hours with ease, or a day or so with effort.
Red - Fight trigger. This is your mental trigger. "If that person does 'x' then I will shoot them." Your pistol may, but not necessarily, be in your hand.