I don't know a whole lot about it, but I do know that breeding white to white often produces deafness. I think that must be the problem with Dalmations with too small spots -- too much white!! A friend breeds Cotons (a rare breed) and some of them have a beige tone to their coats, or beige or grey ears. And so they like to breed these as opposed to the all white ones.
She has one male where the black pigment has not come in all around his eyelids. It's kind of pink and black blotchy. I think this is what happens if you have too much white in the lines.
I had a blue merle rough Collie years ago. If you breed blue merle to blue merle - you run the risk of getting white or blue merle blind and/or deaf puppies. Some irresponsible breeders like white Collies -- I guess they don't care!