Is it sprayed through a stencil? Maybe you could sand back, add more black and then go again?
Sneaky way out that I would do if ever contemplating a black faced headstock is to use decal transfer paper reversed out in that the background would be all black and the image reversed in colour. Easy if all you are doing is text. Alternatively you could just do your image in the desired colour and then cut the sections out individually and affix to headstock that way then clear coats over the top.