First of all, well done on the guitar body - that looks amazing!
As for doing something similar on the bases that come with a Bottlehead kit, I have done something similar in the past. I wanted to get a more interesting finish than a plain stain, so I layered black (think it was actually Ebony) Minwax stain over a lighter color - something in a medium brown. I then sanded with a belt sander to expose the brown (I was going for more of a distressed look).
The grain doesn't rise so much on the Bottlehead bases to have a lot of depth to leave light and dark areas, but I bet a light touch could succeed in achieving a similar effect to your guitar body. I got it to a slight degree on my Seduction base, but, of course, using a belt sander, it had more to do with where and how hard I pressed and how long I dwelt on a post. I also noted that it took a lot of coats of the Ebony stain to get a lot of contrast going, and then I ended up overstaining and finishing with some Watco Oil stain/finish.
I do like the end product, though I plan to try to get something of a blue denim effect on a different project, and I will likely use the same process again to get a match between my new stereo cabinet (grey-brown) and the bases, using the grey-brown under, then ebony over and sand to give some nice contrast but still be color-keyed.
I'll post a phot when I'm back home if there's interest.
