Generally, the copper tarnishes and turns dark and dull. This tarnishing occurs when the copper reacts with the air and a patina develops. The color of the patina will vary with the copper and what it is exposed to. Inside the house, copper will gradually get an antique penny brown color. But if the copper is exposed to water, the patina will gradually develop a bluish green look. The patina protects the copper from corrosion.