North American gray wolves that crisscross the frozen tundra after migrating caribou tend to be light colored, blending in with snow and ice. But dark wolves are common in forests, possibly because there they can slink through the woods unnoticed. Geneticists have pinpointed the gene variant that imparts this black fur and determined that it comes from domestic dogs that interbred with their wily cousins thousands of years ago.
cool. more here.