He may be able to guide you in selection of a safe "in the wood" dye stain. The oak flooring oldtimers talk about using diluted yellow dye stain in a suitable liquid medium in order to approximate that "old yellow" tone of old oakwood. Whatever you use, be careful and test it in a small area or on a sample of the old boards. You probably need to use an "in the wood" dye stain, and also an "over the wood" oil stain in order to get the look that you seek. I've not tried it, but it sounds plausible. You need to get some yellow deep into the wood.