Sound And Color

A student came to the Great Venerable Chan Master Pop-An (Fa-Yen 885-958) and asked: “How should I understand sound and color? ” Venerable Master Pop-An said:
“Here, good Monk, why dont you introspect upon yourself who is asking now? “
Later, Chan Master Ja-Soo sang a Gatha for this:
“Sound and color are merely two words;
The monk didnt realize those sands in his eyes.
Playing the jade flute in the yellow crane gazebo;
In the town near the river, the plum blossoms falling in May.”
How should you understand sound and color?
Jade flute? What kind of jade flute?
Plum blossom? What kind of plum blossom?