Black Dogs are like all BK's, they clean up beautifully. It is like the volume control suddenly started to work! If you think of some of Jimmy page's cleaner tones, like Since I've Been Loving You or What Is and What Should Never Be, then you can get that type of tone (almost single coil sounding).
I love the sound of them, I have them in an old LP, and they just nail the Zep sound.