Source: "Xunzi Persuasion" is blue, taking it from blue, but blue is blue; Ice, water, but colder than water.

Explain in vernacular: Indigo is extracted from Polygonum cuspidatum, but it is bluer than Polygonum cuspidatum; Ice is frozen by water, but it is colder than water.

Li Mi studied very hard and read a lot of books when he was a teenager. His teacher Kong Kun is also good at studying, but a few years later, Li Mi is better than the teacher. At that time, Kong Kun, in turn, asked Li Mi for advice. The students made up a ballad: green turns blue, blue Xie Qing; Teacher He Chang, in the Ming Dynasty.

Cyan: indigo, cyan pigment. Blue: Polygonum blue, a kind of grass that can extract pigment. Indigo is extracted from Polygonum cuspidatum, but its color is darker than Polygonum cuspidatum.

Extended data

The creative background of "encouraging learning";

During the Warring States period, slavery further collapsed, the feudal system gradually formed, and epoch-making changes took place in history. Many thinkers expressed their opinions on the social changes at that time from different positions and angles, and gradually formed different factions such as Mohism, Confucianism, Taoism and Legalism, which were called "a hundred schools of thought contend" in history.

A hundred schools of thought contend and have written many books, publicizing their own ideas and criticizing others, resulting in a situation of "a hundred schools of thought contend". Xunzi was a representative of Confucian school in the late Warring States period. He believes that the existence of nature is independent of human will, but people can use subjective efforts to understand it, adapt to it and make use of it. In order to reveal the significance of learning the day after tomorrow, he created the article "Encouraging Learning".