I wouldn't be as concerned about him getting the correct color as I would about him polishing off rib engraving and other details as he apparently did to Tamid's gun.
As far as the suggestions about mixing wood dust with epoxy as a filler to build up over that nasty checkering, that is usually reserved for a very small area, or to replace a couple checkering diamonds that break off. Epoxy and wood dust as a filler typically leaves the repaired area much darker than the original wood. Even using a lighter colored wood dust such as pine or maple leaves a dark and very noticeable repair on walnut. Grain painting or figure enhancement to cover the discoloration is only on the surface, and the cost of that plus the epoxy body-work and cutting new checkering would likely be prohibitively expensive. I recall seeing a vendor at a gun show who was doing water dip transfers of exhibition walnut wood grain onto fiberglass and synthetic gunstocks, but it was very glossy and wouldn't look at all correct on a vintage double.
http://www.hydrodip.com/photo_gallery/gallery/
