Creating a mobile friendly heat vision like effect

hi. is there any mobile friendly way to create a heat vision effect? like when it’s on i want my enemies to be black(or white) and the rest of the world to be white(or black! doesn’t really matter!) i am thinking about changing the materials but i guess it’s not very mobile friendly?! and my world is static so i guess i can’t change their materials anyways! right?! i’m not sure about post process too! want it to be as light as possible!

we are a sniper and i want the soldiers in the pic to be more visible when enabling this effect. and if there is any other way to highlight the enemies i’m open to suggestions! it doesn’t necessarily have to be like a heat vision!


also if i can create something like this where environment is white and the soldiers are red like engine lod coloration its good enough too. i just want the enemies to be be highlight. if i try to change the materials of my meshes it does’t show up. plz help!