ARBA (American Rabbit Breeders Association) has what is called "Standards of Perfection" for each breed that is allowed to be shown in their shows. (Lionheads just passed their first presentation last year so while they aren't an "accepted" breed until they pass three times- ARBA now is in control of the Standards as far as I understand it - I could be wrong). These standards are published in a book - plus once a year - as new groupings of rabbits are added to the ARBA list - they are published in Domestic Rabbits magazine, which ARBA publishes.
As a lionhead breeder, I currently have two lines of rabbits that I work on. Since only 8 colors are "showable" because they are on the certificates of development...these are my "show" line. The colors are: siamese sable, sable point, tort, REW (ruby eyed white), orange, fawn, chestnut and black. When I work with this line - I aim to get as close to the standards of perfection as I can. These standards tell me what judges are looking for and how they award points, etc.
For my pet line (I have brokens, otters, chocolate, and harlequins), while I try to aim for the standards - I focus more on the personality of the rabbits (I want them to be good natured) and color and mane. These rabbits can't be shown - so I'm not as worried about the shape of their head or the size of their ears or their body type (although I do try to keep them close to the lionhead standards in hopes that one day they will be showable).
I hope I've answered your question. Basically - breeders have to know the standards for their own breeds of rabbits. This means they need to know what the judges are looking for in body type, ears, hindquarters, etc - along with the colors that are acceptable to be shown.
By the way - a pet rabbit is mainly one that doesn't meet the standards. For example - it may have a white toenail or it may have slightly longer ears. It could be that the rabbit has the wrong eye color (although that is fairly unusual). It could just be that the breeder believes that the rabbit won't do as well on the show table as other rabbits so they decide to sell it as a pet.
In my case, I have two lionheads I bought as pets before I ever thought of breeding. They were pets because they have white splotches on them...making them unshowable!