This building is the United States Post Office in Athens, Georgia. It looks so white against the morning blue sky in this June 2002 picture because it is built of marble, almost certainly Georgia Marble from the Blue Ridge of north Georgia. Marble is metamorphosed limestone, and so it is easily cut like limestone. However, because it has been metamorphosed, primary inhomogeneities have been obliterated to provide a rock with much more uniform physical properties, and only vague traces of original layering or structure can be seen (as in the view below). As a result, marble is easily cut and sculpted without breaking, and it can be polished to a fine shiny finish. That's why marble has been used for centuries for building and sculpting. For example, the Parthenon and the other buildings of the (Greek) Athenian Acropolis were built of marble. Here, a (Georgian) Athenian post office is built of the same material, and with a collonaded front inherited from classical architecture like that of the Parthenon.