I had thought of this too, and RJU is right, someone could make all the awps pink in game or some crap to that regard so they always know who has the awps and what not, or a color where ppls guns can be seen thru smoke and or walls and shtuff. Im not familiar with the material walls, thats just what iv'e heard.
Bottom line if the servers were set to sv_pure 0 someone somewhere would do it, and there are other threads regarding this.