What color does {Xuan} in Xuanwu, one of the four ancient beasts, represent?

It was not until the Eastern Han Dynasty that Xuanwu was considered a turtle or a snake. In fact, among the five ancient tribes, the Huanglong in Puyang, Yangshao and Zhuan Xu in the Central Plains is a dragon, the Qinglong in Dawenkou, Heze and Dongfang Mude is a turtle, and the Japanese dragon is a turtle-shaped. Why did the descendants of Qinglong migrate to Japan? The murals of Jiangjun Mountain include both Mude plants and The Sun and the Tortoise. Xuanwu is actually a blackbird [Xuanwu], or a black dog [Xuanwu], or an ancient animal called "Zhen" ("Chu Ci Yuan You": "Calling Xuanwu a genus [Yu, pronounced as Zhen]"), that is, the prototype of Zhu Xi, which seems to be a lizard with gills or a dog with sharp ears, that is, the ancestor of Xia Dynasty, Kan. Because crows, black dogs and lizards all live in the north, crows live in the northeast near Shandong, and it is easy to confuse Xuanwu people representing the north with Qinglong people representing the east, so there are three-legged suns and suns. Xuanwu, a mural of the Western Han Dynasty, still inherits half birds and half dogs. In the Eastern Han Dynasty, it was popular to read the classics back to the ancient times and unscramble the pre-Qin classics at random, which was half turtle and half snake. As for the name, it is actually brave, which means to ward off evil spirits. It is actually a black dog. Of course, the turtle is really carrying the tablet.