Pennies are brown because they are made with copper. Copper is a metal that reflects light in such a way so that it appears brown.
Since 1982, pennies have been composed of 97.5 percent zinc and 2.5 percent copper. Before this, pennies were almost entirely made of copper. Throughout American history, the composition and appearance of the penny has changed more than 5 times. Before 1982, the only other time in American history in which the penny was mostly made of a metal other than copper was during World War 2 when copper was desperately needed for the war effort. Many countries have done away with the penny altogether, such as Canada.