Qin Shihuang was the first emperor in the history of China. He unified the six countries. In order to consolidate the political power, he carried out a series of policies and promoted the development of China's history. Under such great achievements, he also claimed to be the first emperor. Qin Shihuang wore a black robe because he was superstitious. He thought that he was able to unify the six countries and establish a new dynasty because of the yin and yang elements, so he felt that the Qin Dynasty was based on water virtue, which was black. Therefore, in Qin Shihuang's view, only black is his lucky color, which can reflect that the unification of the six countries was completed with the help of God, so the dragon robe was designated as black.
In the Qin dynasty, their clothes were black. Then, as the most distinguished person in the world, it makes sense to make the dragon robe black. Therefore, in the Qin Dynasty, every minister who went to court wore black clothes to show respect for Qin Shihuang, and Qin Shihuang's army and so on were all in black. If there is a color opposite to black where he can see it, he will be severely punished, so it was black in the court at that time.
Yellow robes were really popular in the Sui and Tang Dynasties. At that time, the emperor's robes were all yellow, which is the color of the emperor's robes in our impression.