Hi ya. I did some biology a Uni and I think that the genetic controls for dog colour are much more complex than simple mendellian genetics (
Gregor Mendel - Wikipedia, the free encyclopedia). Mendellian genetics is the simple recessive / dominance genetics we all know about.
There's so much we don't know about genetics - I'd be more inclined to think it had something to do with the particular mum and dad than anything else.
I don't know how relevant this is but in humans - females' eggs start degrading and by the time a woman is in her forties there can be a higher incidence of genetic defects existing in the eggs. Possibly 7 years old in a yorkie equates to 40 odd in a human (about 1/2 way through the average life span). I'm not a breeder so I wouldn't know.
Plastic and rubber are very inert substances. I would be surprised if they reacted with the sperm.