As noted in my post, this is a familial, genetic anomaly or trait. Surely there is a parent who exhibits the same pigment anomaly (though not manifesting in the exact pattern, more than likely). If not, yours is not genetically passed down, since it does not skip generations. I recently came across an article about a new study of piedbaldism. The scientists studied the trait in animal subjects only, but expect the results to contribute to the overall understanding of the genetic mutation in humans as well. It seems that the gene that is responsible for skin and hair/fur coloring can cause a delay or even halt the cells in their journey upwards into the dermal layer of skin or in the coloration of the hair/fur follicle, resulting in the absence of that pigmentation. They found that the patterns that emerged were random, meaning that even identical twins will not have the same patterns of anomalies.
One question to you, then, is - can you trace the lineage that produced your piebaldism? If so, I would love to know about that.
Another subject altogether is, when I looked at your family tree, I noticed that my husband's Weaver family intersects with yours at the Mary Sensery and Oswalt section. He did a DNA test and this connection seems a sure thing. He is a likely cousin of yours. Serendipitious, no?