PHILADELPHIA—The loose change in American pockets could get a bit lighter and take on a new hue.

The U.S. Mint is considering a change to the mix of metals it uses to make quarters, dimes and nickels, a study Congress mandated in 2010 to examine ways to save money. If the materials are altered for the first time in half a century or more, some coins could have new colors and weigh less.

The...