BV is a dominant gene. It cannot be carried and it is not recessive as reported on Coty's FB page. Not even parts of it. It is simple genetics 101. Unfortunately many reputable breeders tried to correct that information and were banned from his site and their posts removed. They did so in a professional and polite manner but were attacked for trying to correct the misinformation that was available to the general public.
This is a direct quote from Bob Gunning, the developer of the BV, the Gunning Black, as quoted in Alice Klines book "Basic Genetics and History of Mutation Chinchillas":
"Many people have been interested in purchasing a black male in the hope of darkening up their herd of standard animals. We are very emphatic in saying this cannot be done. In most cases they are a phase lighter than their standard parent. By the same token, the black offspring in such a mating could very well be much blacker than the black parent, providing the standard parent was dark and had black veiling."
How black or how good the fur quality of the offspring will depend on the quality and type of standard animal mated to the black but the standard offspring show no black - nor do they carry it.
Alice goes on to clarify that the BV is ..."a dominant mutation. In very simple terms, if the animals shoes any degree of the black mutant factor, it carries the black mutation gene. If it does not show any black mutation factor, it is nothing more than a standard gray chinchilla and does not carry the black mutation gene."
I don't know how it could be any clearer than that.