One was the continued imitation of Soviet architecture—during the Cold War, the Soviet Union used blue glass to shield buildings from surveillance by American reconnaissance aircraft, and China directly adopted this aesthetic.
Another reason was technological: at the time, glass manufacturing processes were not yet fully developed. The blue tint often resulted from imperfect purification, and such glass was also cheaper to produce.

This blue glass carried a dual symbolism: from the outside, it appeared mysterious; from the inside, it created a cool, futuristic atmosphere shaped by its bluish tone.