I agree with some of this, especially the part about people being attracted to his teachings because they're looking for "something dark and shocking to mainstream society." But I really doubt people choose satanism as a belief system because they like purple, black, and red, or even pentagrams for that matter. You can find those colors anywhere, regardless of religious affiliation. Incidentally you have listed my three favorite colors, and I think satanism is one of the more ridiculous belief systems out there.
The symbolism of the pentagram was initially rooted in paganism, NOT satanism. When upright (as opposed to inverted) the five points of the pentagram stand for the five elements--earth, air, fire, water, and spirit. The satanists took this symbol and corrupted it, much like the way the Nazis took and used the swastika, (which, if I am not mistaken, began as some kind of Eastern symbol). However it's still an integral symbol used and recognized among modern pagans, not something exclusive to satanism (although unfortunately the two are often confused as a result.)