A sex-link is a mixed breed chicken where the females are one color and the males another, so you can tell what sex they are from hatching and be 100% accurate. They are good layers, will never go broody, and commonly come in three varieties: red, gold, and black, each named after the color of the female. There are several breed crosses used to make sex-links, each one for a different color. Rhode Island Reds are part of the mix for a black sex link, so your hen is probably part Rhode Island Red.