They are worn by Chassidim as well as the Rebbe. Bochurim don’t wear vayse, only shwartze. Those that wear zukken all week wear shwartze on weekdays. Belzer Chassidim wear shwartze on Shabbos and vayse only on Yom Tov, at a child’s chasuna, and a chosson at his own chasuna.. The Belzer Rebbe wears vayse on Shabbos.