According to the "Zhou Yi" records "Tian Xuan Di Huang", Xuan that is black, the son of Zhou Tianzi in the sacrifice of the sky when the clothes worn is black; and Shuo Fang, is in today's Shaanxi, Gansu and Ningxia Border Areas and other places.

The northern long-snout tribes attacked the week, Zhou Wenwang Ji Chang several times to send troops to conquer, repeatedly frustrated, and then sent the famous general Nan Zhong to Shuo Fang to guard the border, "the Son of God ordered me to the city of the Shuo Fang". When Nan Zhong was defending Shuo Fang from the enemy, he accidentally contracted a disease due to an injury, for which there was no cure. A nameless old man gave berries, and he chewed them day after day, and healed himself. When the long-snout tribe was defeated, returned victorious, offered berries to Ji Chang. King Wen ate it, greatly pleased, praised its taste sweet health, is the God of heaven, and then will be the color as the color of the son of heaven.