Apply shader to everything except mesh

I am working on fog of war for my characters using the 2D Dynamic Lights and Shadows. (current state shown below)

The character's sight is represented by the darker area and places you can't see are left unchanged.

What I need however, is the exact opposite - I need everything in sight be normal colours while the objects outside have a dark tint, similar to what most other games using sight mechanics look like.

I am new to shaders and know absolutely nothing about screen effects so any help/guidance with this problem is very appreciated

EDIT: I mistook field of view for fog of war :p