《梦溪笔谈·辨证一》
熙宁年间，京师的贵人和皇亲国戚多穿深紫色衣服，而称为黑紫，与黑色相混，几乎不可分别，这也是一种人们所称的玄色。
熙宁中，京师贵人戚里，多衣深紫色。谓之黑紫，与皂相乱，几不可分，乃所谓玄也。
During the Xining period, nobles and imperial relatives in the capital mostly wore dark purple clothes, which were called black-purple and were almost indistinguishable from black, which is also a color called "xuan".