I have seen and use the color code concept, I just use numbers. 4 is safe 30-50yds out, 1 is danger 8yds to 5ft. Used with my son I ask him to say what he sees in zone 4 at 2'oclock the switch vision to 11'oclock zone 2.
In a real life sd which is the proper fight or flee zone distant, can you see somebody pull a gun and make a dash for cover or exit stage left in 50yds, 30yds, where do you make a stand and fight from. No wrong or right answer just wondering