The color red itself won't tell you much about the origins or nature of gangstalking.

Red is a signal color, if not the main signal color, so it is only self-explanatory for them to use the color red as a main conditioning color . Commonly found natural colors like green, brown, blue and white are all found in nature(think about grass fields, woods, sky and water), seeing a big red surface is something not that common in the history of human evolution, therefore it's a color we perceive as a special signal color(same as yellow or other color hues that are not commonly found in nature) that will gain special attention compared to colors commonly found in the wilderness.

Remember gangstalking is all about psychological warfare making the TI see patterns and associations, even if it isn't the case for this very instant, making the TI perceive certain patterns like color association as threats, cause paranoia and over-analyses, even if a person wearing said color isn't involved in the gangstalking, because the TI has been conditioned by the gangstalkers to automatically perceive every person wearing a certain color as a perpetrator. Same as the hand gestures. Everyone touches their face occasionally, but the gangstalkers make it seem so everyone who touches their face is in on it by making you associate certain hand gestures with negative experience aka gangstalking, while in reality they only conditioned your mind to associate hand gestures and face touching with gangstalking, so you are believed to think everyone who touches their face(and trust me everyone touches their face occasionally out of itchyness or uncomfortability) to be a perp themself, so you are wary of everyone and every person who touches their face, even though they are not part of the gangstalking.

Summary: red is a signal color so perps use it.