Alpenglow is the phenomenon that causes most of the Dolomite peaks to take on a reddish color, gradually turning to purple, especially at dawn and dusk.
This phenomenon is due to the composition of the rocky walls of the Dolomites (formed by Dolomite rock containing dolomite, a compound of calcium carbonate and magnesium).
The phenomenon is especially popular on summer evenings, when the air is clear and the bright sun sets in the west.