Help colouring objects with other objects

Hi, I am making a game in Unreal where the world you start in is greyscale and colourless. Although I want you to be able to colour back in the walls/floor/other objects when they are shot with a projectile.
I really need it to just color in a small part of the wall with each shot, like in a radius of the impact area rather that the whole mesh

There is probably a really straight forward method for this but I don’t really know what I am looking for. Can anyone suggest any techniques or methods that could help me achieve what I want from this? Thank you so much

My take:
a proper material shader applied on the objects. You can fake different colors with a World Aligned texture. You can make individual areas visible by modifying a Mask at run-time via a Render Target function.
You can look up the render target tutorials for more info on that

The brush material is then just tied to the projectile/whatever and it simply affects the opacity mask that reveals the color.

It’s not easy, but this is supposed to be a core part of your game-play so it’s not supposed to be easy.

An alternative is Decals. Every projectile hit just spawns a decal. This will end up getting heavy and impossible if the objective is to color in the whole world.