Beyond the classroom...
Color = status = what you should be doing.
White = unprepared to act = nothing specific, but ideally you will be moving toward mental and physical preparedness as your time in white comes to an end.
Yellow = alert & aware = you should be looking and really seeing the world around you, and you should have a general plan for how you will deal with general, unexpected, non-specific dangers. The general plan may include a firearm; if so, you have it with you and you have prepared yourself to use it effectively if needed.
Orange = specific potential danger spotted = you should immediately begin making a specific plan to avoid or deal with the specific danger. ("Those guys look like trouble. I will cross the street so I won't have to walk past them on the sidewalk; if they follow me, I will ....")
Red = action required = you must act immediately to save your life, either carrying out the plan you just made in orange, or improvising one from scratch (struggling to catch up) if you didn't have the luxury of moving through orange by spotting the danger early.
Note that each step, from white to yellow to orange to red, is relatively small. However, the jump from white to red is huge, and a very difficult one for most people to make.
Doing what is needed at each step -- preparing, observing, planning, and finally acting -- makes the next step easier to perform. You can't act efficiently unless you have planned your moves. You can't plan your moves unless you have observed the situation. Observing the situation does no good unless you are mentally and physically prepared to change it. So each step builds on the last, and each makes the next step easier.
My personal website: Cornered Cat