The Valley Streams Run Deepest Indigo

KOAN:

There was a student who asked a teacher, the teacher was Dalung [lung means dragon, dragon teacher] and the student said,
“This physical body perishes, decays. What is the imperishable, what is the hard and fast body of reality? What is the body that doesn’t decay? This physical body decays, what is the everlasting body of the real?”
And the teacher said, “Mountain flowers bloom like brocade. The valley streams run deepest indigo.”