Its usage is geographically specific, but this article [1] is a decent starting place. Green is commonly used to indicate that a particular vehicle is the comma

Its usage is geographically specific, but this article [1] is a decent starting place. Green is commonly used to indicate that a particular vehicle is the command post for an incident, e.g. for fire fighting. [1] https://en.wikipedia.org/wiki/Emergency_vehicle_lighting https://en.wikipedia.org/wiki/Emergency_vehicle_lighting