The subsun is located just as deeply below the horizon as the sun is above it. It is a pure reflection halo. Therefore, the subsun is white.
The subsun is formed by reflection on the top surface of
platelets that are in a perfectly uniform floating position. The ice platelets act like a very calm water surface, reflecting the sun. The subsun can also be created by doubly oriented column crystals. However, these crystals are rare. Since the ice crystals must be below the observer, this type of halo can only be seen in ice fog or from an airplane.
