I've come to a statement about white socks: The bottoms always turn gray, no matter how hard you try not to get them gray. It's because the real color of sweat is actually gray, and also, if you sometimes wear your shoes with no socks,  the shoes get smelly and ALSO um... the bottoms of your shoes turn gray, and actually when your sweat touches the cloth of the bottom of your shoe, some chemicals leak out and go on the bottom of the shoe.