What are the taboos of the scarlet letter on a black background?

Red paper and black characters are often used to ward off evil spirits.

In ancient times, red symbolizes auspiciousness and has the function of driving away evil. The walls of many palaces and temples are red. Black characters represent driving ghosts and gods, and they have supreme magic. If the symbols are arranged in five lines, red represents fire, black represents water, yellow represents earth, green represents wood and white represents gold.

The Five Elements is a systematic view of China's ancient philosophy, which is widely used in traditional Chinese medicine, geomantic omen, numerology, physiognomy and divination. The meaning of the five elements includes five basic trends in the evolution of Yin and Yang: water (for infiltration), fire (for disillusionment), gold (for convergence), wood (for growth) and earth (for integration). Ancient philosophers in China used the theory of five elements to explain the formation of all things in the world and their relationships. It emphasizes the whole and aims to describe the movement form and transformation relationship of things. Yin and Yang are ancient theories of unity of opposites, and the five elements are primitive system theories.