keep breeding the lighter ones and they'll keep getting lighter. breed back to a black n tan or a leopard and it'll darken them up and maybe add a little more mask.
it's like the amount of spots on a dalmatian or the degree of black on a saddleback.
genetically, the dogs above are all the same color but with variation within. the number of spots or tendency of shade (white/yellow) is going to lean towards average for the greater breeding pool your dog belongs to. if you have a family of dogs that produces primarily light/white dogs your average will be lighter than for the breed as a whole.
