Choir of Menoth
Only the priest is painted all white because he is the "purest".
The acolytes only have a white cloth over their dark robes because the most important thing about them is the scrolls they bring to the battle field. They are not yet worthy of the full on white suit.
It is a bit funny that the priest is the most important figure of the unit since I think the acolyte minis are far better sculpted.