Answer:
The Statue of Liberty looks blue-green because of a chemical reaction of copper (the metal that she is made of) with the air as the years passed on; corrosion took place, hence creating the blue-green look we have today.
Background (useless) Info:
The statue was designed by Frédéric Auguste Bartholdi, and was given by French to Americans as a gift of the alliance between France and the USA during the American Revolution.
