[Ron Wood]

If you really want to try something wacky, here is something I learned after some experimentation a long time ago. Part of the darkening of the wood is due to oxidation. So what I did was apply some dark brown shoe polish and brushed off the excess, then very cautiously used a mini blowtorch to lightly char the patch. Either have a steady hand or protect the original part of the grip with a shield (a thin piece of metal like a tin can lid will do the job). It goes without saying that this needs to be done with a great deal of care and attention. If you burn the wood too deeply you will mess up the checkering or worse. Another application of shoe polish and a light scrubbing with a tooth brush (perhaps another repetition of the flame might be required if you proceed with care and don't try to do it in one pass) and the patch disappeared. It worked for me, I don't know if it would work for anyone else.