There was an interesting article on off color coyotes that hypothesized this:
"New genetic tests show that all eastern coyotes are actually a mix of three species: coyote, wolf and dog. The percentages vary, dependent upon exactly which test is applied and the geographic location of the canine.
Coyotes in the Northeast are mostly (60%-84%) coyote, with lesser amounts of wolf (8%-25%) and dog (8%-11%). Start moving south or east and this mixture slowly changes. Virginia animals average more dog than wolf (85%:2%:13% coyote:wolf:dog) while coyotes from the Deep South had just a dash of wolf and dog genes mixed in (91%:4%:5% coyote:wolf:dog). Tests show that there are no animals that are just coyote and wolf (that is, a coywolf), and some eastern coyotes that have almost no wolf at all. "
As coyotes just did not migrate to the east, but were imported, and as those imports were from the west, where there is not this type of coloration, even if there are browns to pales, the conclusion would be these coyotes are human generated breedings, which apparently escaped or preferred their wild status to the kennel. It is interesting in the German Shepherd appears to be the base for the thicker fur. They appear resilient thought in Alabama in the genetics are dominating in the melanistic as nature dictates.