For those of you who have an application requiring a black nut you now have a bone alternative.
https://www.stewmac.com/luthier-tools-and-supplies/materials/nuts-and-saddles/black-bone-nut-blank/I do have some concerns though especially after reading the statement where StewMac is recommending washing one's nuts... prior to installation on a guitar to prevent any of the black color from bleeding onto the mating surfaces of the guitar.
As you know some makers install the nut prior to finishing with Martin being one of them, Gibson as well. It's a look, finished on nuts that I like and it's also something looked for with the vintage guitar collector community where originality is king.
I do wonder if washing one's nuts... is good enough when a nut is installed on an unfinished neck and then the neck is shot with solvent based finish. Might be a good idea to purchase some sacrifice pieces of these and do some testing before finding out that the color is not as fixed as we had hoped.
Lastly I've used black Ram's Horn before when I needed black nut material and it was disappointing. First horn material and I speak of antlers is often very soft and not at all as long lasting as bone. Can you say toe nail...... because that is what's it's like only black.
Next when you polish your nuts... to a high shine as I do black ends up looking just like shiny black plastic. This led me to unbleached bone where the bone is harder anyway not going through the bleaching process but it still looks.... organic without the glaring white color.
I'll be interested to see what anyone who tries these out discovers and reports hopefully back here.