Here's why:
* Color genetics: Border Collies have a complex coat pattern inheritance, involving several genes. White coloration is usually associated with the "piebald" gene and can occur in various combinations with other colors like black, blue, red, or brown.
* Breed standard: The American Kennel Club (AKC) breed standard for Border Collies allows for white markings, but a fully white dog is not typical and may not be considered "standard" by some breeders.
* Selective breeding: Breeders usually focus on producing puppies with typical Border Collie markings (black, white, and tan), so pure white puppies are less likely to be intentionally produced.
However, it's important to note:
* Some breeders: Some breeders may specialize in producing specific coat patterns, including white.
* Genetic mutations: There's a chance a fully white Border Collie puppy could be born due to a rare genetic mutation, independent of typical coat inheritance patterns.
Ultimately, finding a pure white Border Collie puppy is a matter of luck and searching for the right breeder. If you're set on a white Border Collie, it's worth contacting reputable breeders and asking if they've produced any white puppies in the past.