I used to do cabinet repair and touch up for music companies in Rapid City SD, and KC Mo. I can promise you there are as many different color blacks as there are whites.
I once worked on the side of the keyboard bed on an upright that was gloss black for about 4 hrs and could not get the finish to blend. I called into the office and told them the problem I was having and they had another tech in the same area with years of experience.
When he arrived and looked at what I was trying to do he snickered!
His first words, " you will never get that to blend because you are using to different color blacks." He then showed me how to do it and had it done in 10 minutes.
I don't know if this will help you or not, but this is how he did it. He scuffed the whole endblock, painted it with black touch up lacquer, waited for it to dry. He then feathered the edges where the new color black came into contact with the old color black and then proceeded to buff. You could not tell any difference in the two colors when he finish and he explained to me it had to do with reflection and the way the eyes work.
If you have a area that can have a hard edge, you just might get the colors to work that way.I hope this helps.
edited to add: I went back and looked at your pic again. Do you see the difference in the reflectance between the new and the old? I also thought I saw a volute. If there is one, that would be the area to paint to, but do the whole peghead. Of course there is always the option of trying a couple more blacks too!
Mike