What is the name of the instrument on which the famous song "Three Plum Blossoms" is played?

Flute or xiao music, later adapted for the zither.

"After Huan Yi's death, "Three Tunes of Plum Blossoms" was widely circulated until Yan Gu, a famous zither master in the Tang Dynasty, changed "Three Tunes of Plum Blossoms" into a zither piece of the same name. In the Ming Dynasty, Zhu Quan included "Three Tunes of Plum Blossoms" in the collection of "Magical Mysteries" and changed the name of the piece to "Three Tunes of Plum Blossoms". "