Use the word russet to describe things that are a reddish-brown color, like autumn leaves or your cousin's pretty auburn hair.
The adjective russet is great for talking about a particular color — in fact, the most common kind of Idaho potato is the Russet Burbank potato, named for its russet-colored skin. In apples, the word russet doesn't apply to color, but instead to a roughness in the skin. Another meaning of russet is a cheap, rough blanket worn in the Middle Ages by poor people. The root is the Latin word for "red," russus.