Looking back on some of the other photos of 'yotes you've posted, it appears many could be considered "Quad-Colored" as it appears many have a combination of white/brown/grey and black. Just a different amount of each.
Folks that know animal husbandry, especially those raising animals for fur, know that the genes for determining color are few, but relate to combinations plenty. Selective breeding can result in pure forms of color and breed standards. Breeding which is done in the wildi is done mostly by animals that dominate and survive. Sometimes color influences this and thus, thru evolution, we end up with animals that generally are always similar colored. Would be interesting to see how much color influences 'yote survival and if certain coloratios in different areas are a result of it.
