Origin: the "Five Virtues Theory" believed in in the early Qin and Han Dynasties.
In ancient China, there were five parties in the southeast and northwest, belonging to the five virtues of wood, fire, gold, water and earth, each with five colors of green, red, white, black and yellow.
The theory of five elements and five colors has a strong superstitious color, but ancient ancestors built a complex and mysterious belief system based on it, combined with the changes of the four seasons and the growth law of all things at that time.
On this basis, the Yin and Yang scholars in the Warring States period founded the theory that "five virtues begin at the end", which was accepted by the public at that time.
"Lv Chunqiu" records:
"Every emperor will prosper, and heaven will see the people.
When the Yellow Emperor, God saw the big cockroach. The yellow emperor said:' rustic spirit wins!' The earthiness wins, so its color is still yellow, and its content is earthy.
In Yu's time, God didn't kill plants in autumn and winter. Yu said: "Wood is full of vitality!" Wood is full of vitality, so its color is Shang Qing, but its business is wood.
At the time of soup, the golden blade was born in water. Tang Yue said:' The banner won!' Gold is full of gas, so the color is still white, and business is gold.
At the time of King Wen, God saw the fire first, and Hong Niao held the book of Dan in the Zhou Society. King Wen said; Internal heat will win! Internal heat wins, so its color is still red, and its content is fire.
The substitute of fire will bring water, and the sky and water will prevail. Water vapor is abundant, so its color is still black, and its substance is water. "
Starting from the Yellow Emperor, the change of rulers in past dynasties was made by God's will, and the five qi rotated. At that time, the Zhou Dynasty was a fire, and the substitute of fire must be water.
Hanshu records:
When Qin Shihuang acceded to the throne, he still said:
"The Yellow Emperor's virtue is the humble opinion of Huanglong.
In Mude in summer, Qinglong stops in the suburbs with lush vegetation.
Yindejinde, silver light overflows the mountains.
Zhou de's fire virtue has a symbol of red and black.
Today, the Qin dynasty changed to the Zhou dynasty, which is the time of water virtue. Yesterday, Duke Wen went hunting and won the Black Dragon. This is the virtue of water. "So Qin changed its name to" Deshui ",taking winter and October as the first year, the color was still black, and the degree was six, with a loud voice, and everything was unified in law.
Rulers of past dynasties always packaged their superiors as destiny.
It doesn't matter whether Qin Wengong really won the Black Dragon. Qin Shihuang found the reason why Qin replaced Zhou Dynasty. He overthrew the rule of the Zhou Dynasty, not by deviance, but by devotion to heaven. Since then, the Qin Dynasty has become the orthodoxy of the world.
To sum up, Qin Shihuang adopted the "General Theory of Five Virtues" of Yin and Yang, and explained to the world that the Zhou Dynasty in Qin Dynasty conformed to Heaven. Because the Zhou Dynasty belongs to fire in the theory of five virtues, the Qin Dynasty belongs to water virtue, and because water virtue is still black, so the Qin Dynasty takes black as the positive color.