Why do Jews wear white clothing on Yom Kippur?
According to custom, we wear white ONLY on Yom Kippur (not Rosh Hashana, Hoshana Raba or Pesach night). One reason is because the High Priest wore pure white garments only on Yom Kippur. According to the custom of wearing white the other times too, it is to indicate either the purity of the day, our angelic status on it, or both.