Why is Guan Yu's face red?

This is a historical exaggeration. It is said that Guan Yu blushed, which actually symbolizes his loyalty and highlights his extraordinary appearance. It is the simple description of his appearance that has shaped his overall image, and we can see the ingenious methods of historians or writers.

For another example, Liu Bei's hands are knee-high, his eyes are full of gods, Zhang Fei's mane is upside down, his eyes are like two bells, and Sun Quan's purple mane is blue-eyed, all of which impress readers by their appearance, but do they really exist in practice? I don't think it's possible, so I can explore that Guan Yu's face is "written" red!