Green is used synonymously with Safe for a surburb status with very few zombies. The name has been derived from the Danger map colouring these areas in green.
Downsides for survivors in green suburbs are widespread overcading plagueing many entry points (Fiddler's Green Syndrome). There's also often widespread trenchcoating along with PKers leeching off the local resources and revive points (both particularly near malls).
While ferals might potentially find a lot of food in such areas, they have a hard time to thrive in green suburbs. Many buildings are extremely heavily barricaded and well-manned, leading often to real-time rebarricading and swift ejection. The lack of nearby zombies also means few and slow reinforcements by groaning, unless a Bellow can reach to nearby unsafe suburbs.