Wechat avatar means sunset glow.

Sunset as an avatar means nostalgia. Colorful clouds often appear on the horizon around sunrise and sunset in the morning and evening. The morning glow and sunset glow are caused by the scattering of light by air. When sunlight enters the atmosphere, it will scatter when it meets atmospheric molecules and particles suspended in the atmosphere.

These atmospheric molecules and particles themselves do not emit light, but because they scatter sunlight, each atmospheric molecule forms a scattered light source.