Why are the Antarctic mosses growing in highly exposed sites brown or red in color?

The purple red moss of Antarctica shares a secret with the leaf that turns slowly from green to yellow- brown. The secret lies in their pigments. Pigments are the natural coloring matter of animals and plants. Chlorophyll, the pigment that gives the green color to leaves breaks down, leaving the leaves yellow brown. A yellow brown leaf is rich in Xanthophyll pigments. 

Xanthophylls are useful to plants as they help to reflect away the harmful ultraviolet rays of the sun. Antarctic mosses that grow in sites highly exposed to light are rich in xanthophylls. So, the leaflets turn shades of red or brown, adding color to Antarctica.