Mine opinion about the wood used for the wranka is:
SPALTED TAMARIND - (Tamarindus indica) Also called Tamarin.
(text from the net)
Spalted Tamarind is a beautiful wood from Laos, Southeast Asia.
Much of this wood comes from logs that were either found on the forest floor or were cut and then allowed to spalt in the very damp warm conditions of the jungle. The colors and various line patterns are truly unique from one piece to another. Heartwood has a spectacular back ground colors of ivory, yellow, and black lines, which gives this such unpredictable landscape effect.
My guess about the pendok discoloration is that he had once been exposed by any acid / salty influence, that gives copper a brownish color.
But it may also be that this chemical is produced and then coated.
I would leave it as is but that's my opinion, and if you do not like it then you polish.