is there a name for them.??
Yes - mixed breeds. A possibly more charitable term is "mismarks." Your black isn't a purebred, or at least, there is an out cross somewhere in his fairly recent family history. The gene that causes that color is called Himalayan, after the Himalayan rabbit breed which is apparently the oldest breed to be that color. The very popular meat breed called the Californian was created from crossing Himalayans with Chinchilla rabbits, and New Zealand Whites.
Just what that color is called depends on the breed you are talking about. In a lot of breeds, the color is called Himalayan, or Himi for short. In other breeds, it is called Californian, and in yet others, Pointed White. Confused yet?
The California was used to help develop the NZ black variety
Ummmm, I'm sorry, but you seem to be a bit confused. The breed is called
Californian. "California rabbit breeders," which I assume you saw somewhere, means "breeders of rabbits that live in California."
The gene that causes the Himi/Cali/Pointed White pattern is dominant to the one that causes REW, so this had to come from your black buck. As long as this breed has existed, there is no longer any reason that the Himi gene would be in rabbits of 100% pure NZ blood, so
technically, your buck doesn't qualify as "purebred." Understand, though, that "purebred" is a relative term. Rabbit breeders do out crosses to other breeds all the time, for a variety of reasons. The most common reason is to improve type, though since the NZ is considered by many to be pretty much the perfect meat rabbit, I doubt it was that. There are a number of breeds that this gene could have come from; the Satin, the Rex, the Altex (just to name a few). Most likely, though, it came from a cross to a Californian - people often cross NZ's and Cali's because of the "hybrid vigor" in the offspring.
So, someone somewhere along the line blended something else with a New Zealand. As long as the type is close enough, most meat breeders won't care. Even in show rabbits, this sort of thing is done; I once had some pedigreed Harlequins that threw the occasional REW (obviously, there was a NZW somewhere back there). I jokingly called the white ones "paint-by-number Harlequins;" though the white ones were basically useless, the cross that had introduced that gene into the Harlie gene pool had also given that line awesome type (something the Harlequin sorely needs!)
Anyone who knows meat rabbit breeds will know that "pure" NZ's don't come with points, so this may or may not cause an issue for you when it comes to selling them as purebreds. These particular rabbits have small, light "points" because they have one Himi gene and one REW gene; if you breed one of them to another REW, some of the offspring will be REW. Those, when bred to REW's, will only produce more REW's; whether you want to go to that much trouble to avoid awkward questions is up to you. Of course, you could simply replace your buck with one that
won't produce non-breed colors.
