Copper
Copper is one of the few coloured metals. Most metals are gray or silver. Gold, copper, caesium and osmium are the only four coloured metals. Copper is green as copper(II) carbonate and copper(II) hydroxide. It turns green because it oxidises. After a time in the air, copper forms green copper carbonate at the surface, called verdigris. That is why the copper roof of a building looks green.