This sounds like a job for a post process material. You make whatever effect you want in a material and set it to be a post process material.
Then, to know what you want to apply this effect to you check the distance to the player in the ENEMY blueprint and if close enough enable draw to custom depth in the blueprint. Please refer to this link for more info.
(OSX.) (C++ or blueprints work.) I’m trying to make a system so when an AI element is close to the player, there could be a distorted black and white or red effect on the camera. When a good distance is created between the both the effect vanishes. Any help would be greatly appreciated!