Your broken buck will throw more brokens if bred to either another broken or a full color rabbit, so you can follow the rules for breeding a black as it pertains to mixing any of the other colors with a black rabbit, then consider if you want only broken offspring or if you also want full color. You also need to consider what you will do with the offspring, as there is a potential for unshowable colors.
A true broken carries one copy of the dominant broken gene (En) and one recessive copy (en) to give it the geneotype Enen.
If you breed true broken to true broken (Enen x Enen), you will get Charlies (EnEn - very lightly marked brokens), brokens (Enen), and full color (enen) kits. Brokens with too little color are not showable, but can possible be used in a breeding program. You just want to make sure that you are using a true Charlie that has good patterns behind it. There are such things as "False Charlies" which are genetically true brokens (Enen) but have too light of a pattern to be desirable. You want to avoid breeding with False Charlies and perpetuating poor patterns. The problem is it is not always possible to tell by looking if the animal is a False Charlie or a true Charlie, so the understanding of genetics and test breeding is very helpful.
I would also recommend if your desire is ever to try and breed show quality animals that you try and purchase true show quality stock from a reputable breeder that is focused on breeding to the Standard. Breeding up to show quality from animals that just don't have the genetics to begin with is really not probable. I won't say it's impossible, because theoretically you could do it, but it isn't likely and would be much easier to start with quality stock to begin with. You don't have to spend a ton of money either. One of the best things we have done is purchase some quality brood does from breeders that have used them and gotten offspring that are better to keep themselves, but are still good breeders.
