Does anyone use their bark for purple dye once its depleted?

I've seen a photo of someone who had used their soup to dye a shirt. It was more of an iron-oxide-brown than a purple. Might could stretch and call it maroon.

I think the colour is destroyed once you basify it.
On the other hand, increasing the pH makes the colour very red. Only the raw powder seems to be purple.
Maybe I'll try it someday.