But he couldn't find what he wanted in two places.
Meaning: blue sky: the sky refers to the heavenly palace;
Yellow spring: underground spring, which refers to the underworld.
Sentence meaning: For example, I have looked everywhere. Describing Yang Guifei's death, Emperor Tang Ming missed her very much, so he sent an alchemist to look for her in the sky and underground, but he found nothing in both places. Suddenly I heard that there is a fairy mountain on the sea, and Yang Guifei is there.