Zone Ratings are the official state of a given area. They were created in 1969 by an English college professor, named Warren Pike. There are 8 categories of Zone Ratings, rated in danger by the darkness of the colour the area is given:
White Zones: The safest areas in an undead outbreak. There are almost no infected in these areas, and thus, they are very ideal for evacuation zones. They are very prone to overcrowding, and being downgraded to other colours, as many infected refugees flee to the nearest White Zone.
Cyan Zones: The second safest areas in undead outbreaks. While there are typically more undead than White Zones, usually Cyan Zones are given higher priority in troop allocation, as White Zones are often guarded by civilian millitia, because that is all that is needed.
Yellow Zones: These zones are oft referred to as the line between the "Safe" Zones and the "Conflict" Zones. They are the zones that White Zones almost always degrade to after infected refugees who have managed to pass security die and reanimate. Yellow Zones are the most common zones for undead outbreaks sites to be, as there are still more humans than undead, but the undead are much more numerous than in White and Cyan Zones.
Yellow-Green Zones: The first of the "Conflict" Zones. They are constantly being upgraded and downgraded to other Zone types. It is rare for a Yellow-Green Zone to stay that way. There are very few examples of YG Zones.
Orange Zones: The second Conflict Zone, this was the state of Europe during the early stages of The Undead War. Orange Zones are very unsafe, and are the tipping point between human-controlled zones and undead-controlled zones. Casualties are high, and civilians are virtually unheard of, either dead, undead, or evacuated.
Orange-Red Zones: This is the first zone where the undead have a majority. Human forces are almost always on the run in OR Zones, or they are classed as "expendable" units, or they are trapped and unable to escape. They usually cannot be saved until several months after they have been lost.
Red Zones: The "disaster" zones. Humans are rare, the undead are everywhere, and social order is all but gone. Stories of Red Zones being brought back from the brink are unheard of.
Grey Zones: Grey Zones are zones where all organized human resistance has ended. Western and Eastern Europe were very much like this during the middle stages of the Undead War, save for Italy and a few isolated pockets.
Black Zones: The peak of undead infestation. Almost no humans are in these zones. They are often the result of massive battles between the undead and humans, such as Leningrad. Russia during most of the 1940s was a prime example of a Black Zone, after the initial fighting.