I've heard people say you can mix sawdust from your workpiece with wood glue to make an invisible patch, but I've tried it twice (once in oak, once as pictured on ash) and both times it came out significantly darker and the surrounding wood. The glue is Tite Bond 3.
Does a different glue work better? How wet should the sawdust paste be? This is on the back so it doesn't matter a lot, but I'd like to have a good process for filling little mistakes.
Looks like you've got it figured out, but I'll add that this is exactly why I Keep titebond 2 and 3 handy in the shop. 3 is great for Walnut and darker exotics whereas I use 2 more when working with paler species. Titebond 1 is an ugly yellow abomination everyone should stay far away from.
ETA: Also baby wipes are a godsend in the shop for cleaning up glue where you don't want it. Combined with a dry towel afterward you can make life so much easier on yourself by just cleaning the glue while it's wet. It took me over a decade of chiseling off dried squeeze out before I started taking glue up cleanliness seriously. But I'm a slow learner, you don't have to be 😉
Good luck in the shop my friend!