There's several species of wolves with differing color tendencies. The Southern red Wolf was named obviously because it's a red species. The Arctic Timber wolf is usually grey although as you say black is beginninig to show up occassionally. However most biologists believe it's through interbreeding with domestic dogs (although since the trait is persisting it obviously must be good for their survival rates) White is an anomally and is rarely (if ever) passed down as it hurts their survival chances.
Officially there are in fact only 2 species of wolf canis Lupus ( grey wolf) & canis rufus (red wolf) although some researchers claim that the Eastern timber wolf (canis lupus lycaon) is ia seperate species but the jury's still out on that one. The variants such as , timber, arctic, Iberien etc. are sub-species.
Wolves range in colour from white through to coal black passing by greys, yellows,tans, browns,golds, reds & mixtures of all of them, even pie wolves have been seen.. Arctic wolves (canis lupus arctos) are usually white, Canadian & Alaskan wolves are usually grey or black & European wolves are mostly greyish brown..
Unlike dogs, a wolf's coat is rarely uniform in colour.
Before the arrival of man, wolves were the most wide spread mammal, occupying most of the northern hemisphere. Helas, quite a few other sub-species are now extinct.
