The grey area is the container for the Light and Shadow Realms. It is grey, due to the fact that it must have two ends of a spectrum. It represents what two opposite ends produce. No other colors can exist here, and no light can enter or be produced within the Grey area.
Limbo[]
It acts as a sort-of limbo or out of bounds state for any object within it. Time does not fully exist here - you can move around, but you wont ever starve. Most people who have gone here return mentally broken, because they have spent, in their perspective, millennia.