How to make certain sections of a level grey scale at runtime.

I’m working on a game for a school project, what I require is that when one of the players walks in a certain area that area will be coloured, while all other areas are rendered in black and white. Would that be possible and if so how?

(I’m using unity 5.)

Thank you.

Put a volume around each area and do collision detection to decide which area the player is in. Modify the area’s material to change it’s colour: