kfb: You say that you understand the dress code of black and white, velvet yarmulke…
I’m sure you don’t think that Hashem said people must wear black and white velvet yarmulke…, so why do you think Hashem has to say people shouldn’t wear thick black glasses in order for there to be a reason people shouldn’t wear them?
I didn’t read this article, but if what you are saying is true, I think the reason is obvious. The more a person – especially a man- is invested in something like fashion, the less he is invested in ruchniyus. The aim of this chassidishe school is to raise Jews completely invested in ruchniyus. Ergo, they ban stylish things, in order that their children don’t get attached to them.