Color grading
A post-process pass that remaps the frame's colours through a lookup table to set mood — the game engine's answer to a film colourist.
After the scene is rendered and tone-mapped, colour grading comes last: each pixel's RGB is looked up in a 3D LUT (a little colour cube) that shifts the whole palette cool, warm, bleached or saturated. A single table can turn a sunny level into a cold dawn without touching anything in the scene itself.
The idea is lifted straight from film colour grading, and artists can often export a LUT from Photoshop or DaVinci Resolve and drop it into the engine. Unreal Engine 3 (around 2007) made the technique common in games; today it is a given in every post-processing chain.