Well, if you want to know a little more, have a read of this post by Marimat: White boxer breedings
And here's the rest of the thread: White boxer breedings
Technically, that's a discussion about the breeding of white boxers and the effect on the whole population that would occur by further dilution of melanin by breeding dogs with two copies of the extreme white spotting gene (Sw). But the same principle (albeit to a lesser extent) applies to the breeding of flashy dogs together, which carry one copy of that gene - we get dilution of melanin, affecting both coat colour and organ pigmentation. Repeated breedings of that type result in diluted populations - where the coat colour is commonly a pale tan and unpigmented haws occur even on 'plains'. In other populations, where flashy dogs are less commonly bred, neither of those are common occurances.