Leaves changing colors is one of the most iconic parts of autumn in the United States, and there's still time to catch stunning fall foliage before trees become totally bare leading into winter. But ...

This is the time of year when Nicole Hughes gets constantly distracted by the fall foliage as she drives around North Carolina. "I'm always looking," says Hughes, a biologist at High Point University.

Scientists know why leaves turn yellow in the fall: Chlorophyll breaks down, revealing the yellow pigment that was there all along. But red? Red is a different story altogether. Leaves have to make a ...