John Asks:
I’m trying to get a black or dark gray finish on the face of a titanium driver head. What voltage achieves that color?
Sorry, John. Anodizing produces a particular spectrum of colors limited by the first two octaves of optical interference. I explain it here.
Black and gray are shades, not colors. One cannot make titanium black by anodizing.
So, how is black titanium made? Everyone who does it is keeping the actual process a tight secret. But my educated guess is that it is produced by implanting nitrogen into the titanium using an industrial vacuum effusion furnace. This produces a relatively thick layer of titanium nitride in a similar chemical manner that titanium dioxide is made by anodizing. But nitrogen implanting cannot be done in an oxygen rich environment, like air or water. Air is 21% oxygen by volume, and water is 33% oxygen by atoms, or 88% by weight.
The Mrtitanium Forum 
To obtain a dark gray, your PH needs to be greater than 13. You will get a wht anodize layer that will need to be removed to reach the gray. This is a military anodize and the details of the process is highly protected.