Like Stan, I was also in awe of some of the virtually invisible repairs done by some stock repair specialists. That was what prompted me several years ago to do some tests of various adhesives. I planed some walnut and glued pieces together using a couple of PVA wood glues, cyanoacrylate, polyurethane glue, and several different epoxies. Then I sanded and finished the glue joints with various finishes. Titebond II wood glue gave me the best results with a well fitted joint.
Fitting and correct clamping is extremely important. If you count on any glue or epoxy to fill a slight gap, that glue line will be very visible when the finish is applied. No dye or color is going to help much. But even a perfectly fitted patch may stick out like a sore thumb if the patch does not match the parent wood. So I also keep a large box of different walnut scraps from various species of walnut. When doing a repair, it pays to spend some time to find a piece that has the same color, grain, figure, and pores as the stock I am repairing. Another trick is to use the point of an X-acto knife to artificially extend pores across the repair joint.
