
Here's a commissioned painting I finished some time ago and I wanna share a few tips regarding it
Using saturation to shift color temperature
I color picked some areas in the image to show how completely gray colors act as cools in this context, and they would have been warm if the overall atmosphere was cold.

This is something you've probably heard a lot, but I figure it's useful to see the actual colors on the color wheel.
Use spot lights for composition
A cheap and very effective trick is to place spotlights or cast lights to create focal points (in this case, the light appears to come from an opening in some building out of frame, but you don't even have to justify it). You can play with different spotlight colors for different effects, and you can also do the opposite - have a cast shadow or light fall-off to punch out a character against a brighter background.