there is a reason that you will be less likely to find any responsible breeder producing a rare color, show breeder or not. rare colors tend to be recessive and that means that not only will you be doubling up on those color genes to get what you want but all of the other nasty skeletons in the genetic closet. Most health problems are recessive. Allergies, skin issues, eye problems, even cancer risk will be increased.
Since the color is not common, you have less dogs to choose from for your breeding program. That means other issues have to be overlooked to insure that you get the color you want - the first to be bypassed is often temperament. Instead of breeding the best of the best dogs to produce the next generation, you have to use "almost as good" dogs simply because they have the color you want. The next generation you have the color a bit more common but you've already doubled up on all of the health issues as well. You'll have more inbreeding since so many dogs that share the recessive color gene will have common ancestors. Plus, the easiest way to cement a recessive trait into a bloodline is through close breeding of parent/child, brother/sister, etc
Agreed. Inbreeding usually leads to health problems.