I'm a little late to this convo, but this very thing occurred to another customer of SV recently who had used ISO on their Fusion stem and saw the same bleaching and leaching of pigment. I reached out to Vu to confirm that no dye, stain, or other product is applied to the wood to colour it. He confirmed that they only use a natural oil and beeswax/carnuba to finish. They are well aware of the risks of applying any type of colouring product to a vape stem. So what you are seeing is the pigment of the wood and perhaps some left over fine particulate being stripped away by a solvent.Oil that up and it’ll look red again to me that looks like pigmentation from the wood, although definitely more prominent than mine but still the same hue nonetheless. That faded look on the wood after you rubbed it is what wood looks like stripped of the waxy / oily finish.
I get brown stains when I wipe the mineral oil off my Firewood when I clean it too. And my Walnut Vapman. It just comes down to the wood.
Something else that can happen I think, if an oil rich finish is applied too thick without polishing it off, it can also cause the pigments to leech the longer it sits. But that’s probably reaching on my part.
I’d wax it up if I were you, and go through a couple cycles, it shouldn’t be coming off on your hands.
Edit: Just read back and saw you confirmed with Vu, as well.. apologies for the echo.