Dark Pied is sometimes used/defined differently. My original understanding what it meant was a bird genetically pure for pied. Visually, most of them have white limited to chin/wingtips, maybe with a couple white feathers elsewhere, but the main point was it's a genetic definition. One of the supports for this was how people used to say 'if you breed a dark pied with a white, you will get 100% loud pied offspring'. (loud pied are genetically half white half pied, so this result is possible only from a pure pied bred with a white; all chicks would be half pied half white, genetically) For this one, dark pied x dark pied= all dark pieds.
Lately it seems dark pied is being used for pied birds with not much white(example: small white patch on wing, neck, either no or only a few white feathers in the tail) but not genetically pure pied, unlike the above. For this one.. if both birds are pied without much white(not genetic pure pied) the result is same for loud pied pair- 1/4 white, 1/2 pied and 1/4.... dark pied, as in pure genetic pied. White chicks would be the proof the parents were not genetic pure pied.