What does the idiom "blue sky and yellow land" mean?

Blue sky: Taoism says that the first floor of the east building is full of blue sky, which is called "blue sky" and refers to the sky in general.

Death: In China Taoist culture, it refers to the place where people go after death, that is, the underworld. Death is also one of the nine prisons and nine springs. For the dead, the water turns yellow when the well is deep, and it is buried underground after death. Therefore, the ancients regarded the dead zone deep in the ends of the earth as the underground world where people lived after death, generally referring to the underground.

Blue sky and yellow land refer to the sky and the earth and every corner of space.