I find it so interesting that everyone has a specific " black" in mind.
To me, the overall appearance and feel is more important than trying to "match" a specific prop color or tone since actual paint colors used, no matter what it was, was altered by lighting, film and age.
If you used the exact same color paint I doubt it would look like the real prop unless you "aged" it.
Every color, every surface on film, which is the minds eye, is changed on film due to reflections, shadows and processing. Repainting and touch ups add to the ball of confusion.
I personally do not think the " intention" was to have 3 colors on the phaser. I think it was intended to be visible and noticeable on film. Dark P1 and grip, lighter P2 body for contrast. I have doubts that the grip was intended to be bronze colored...unless it was specified in the design drawings that the handle should be bronze.
The black was meant to be black, and while there are different shades and tones you can only ever match one specific frame of film at a time. The idea to me is to get close to the overall effect which Wand did. As they said, they matched the color of the 50 year old paint to the way they saw it on the day they examined it.
Under the right lighting, I'll bet it will look strikingly like the best stills we have of the heros in action.
That said... Maybe a little tinted wax...or brushed on clear lacquer to add the ridges of the brushed on paint of the real prop?