What is the symbolic meaning and moral of the scarlet of the Forbidden City wall?

The first layer means that red stands for wealth and yellow stands for auspiciousness. This is a common explanation.

The second layer means that red five is fire and yellow five is earth. Under the fire, there is fire on the soil. Shangji

Supplement cinnabar

Cinnabar is a traditional color name in China, also called China Red, which is between orange and red. Made of opaque cinnabar. Because the real cinnabar comes from China, it is also called China Red.

China seal is printed with cinnabar paste, and cinnabar pigment is also used in China scarlet paint. In Taoist culture, cinnabar is regarded as life and eternal color.