Cyan: Indigo, dark blue dye. Blue: Polygonum indigo, the name of grass, is used as a blue dye. The original meaning is that indigo is extracted from the indigo plant, but the color is darker than the indigo plant. It is a metaphor that students are better than teachers, or later generations are better than predecessors.

"The green is better than the blue and is better than the blue" comes from Xunzi's "Encouragement to Learning", a Confucian scholar. It is a common saying that metaphors people can improve after learning or education. It is often used as a metaphor for students to surpass their teachers or for future generations to be better than their predecessors.

The meaning of the idiom 青 comes from blue and is better than blue: Qing is extracted from blue grass, but the color is darker than blue grass.

Green, taken from blue, and green from blue; ice, derived from water, and cold from water. ——Xunzi.