If you're trying to repeat what you see on the Mayones, I'd stain the entire bass black, sand it back until only the open grain on the ash is still black and then hit it with the burgundy stain.Yeah, I've seen it too. But there are loads of ways to do it, and I'm not sure what the best route is for my desired look.
Anyway...filled the void in the back:
Seems like a fool proof method to me. I like how it's looking and that epoxy fill will blend in pretty well once you get some black on there.
EDIT: F-bass . not Dingwall that uses that finish regularly. I knew it wasn't Dingwall, but it was bugging me.