You can wear black when attending Xinjiang Kazak wedding. The marriage customs of Kazak people vary according to regions and nationalities. Generally speaking, you need to wear formal clothes to attend a wedding. Men usually wear traditional Kazakh costumes, usually black or dark robes, robes and trousers decorated with traditional Kazakh hand embroidery and tied with traditional Kazakh ribbons. So you can wear black for Kazakh weddings in Xinjiang.