I will come look you up if this time fails and I have to strip it back down again. The gray color is on maple. The beech takes a brown from it that is not dark enough to yet to be a stand alone stain, but it cured some of the problems the beech presents. It will darken all of the wood like you said the aquafortis solution does. It isn't strong enough alone, but it helps take the spotty look away quite a bit. The other thing it does is something to the wood. After multiple applications of the vinegar, once cleaned up well and given time to dry, the beech will now take stain where it would not before. It is good enough to start finishing it now, but I want one more shot at working two places out! I agree it can be a nice looking wood. This this one looks very much like some walnut you see right now.
Read the other thread I posted. The implications of being able to adjust your color thru your first coat of oil could prove a life saver.