It's a color phase they go through during the course of the year. Long-furred canines do the usual amount of routine, year-round shedding. And as old shafts of fur are shed, new ones replace them. Routinely (being an owner of two Australian Shepherds, I can speak from vast amounts of experience in that regard. ). Wolves which may appear in a light tan agouti coat (the standard gray wolf coat) at one time of the year can appear in dark phase another. And some seem to retain one or the other color routinely. It seems to vary from wolf to wolf.

So just to clarify, a dark phased wolf is more less a temporary thing? I'm not very familiar with the term.

Those are just gray wolves in dark phase. Their coats go through color changes through various sheds. I've actually seen Alaskan and Canadian (and U.S.) gray wolves from a single pack showing a variety of coat colors, including the dark phase. Even at one particular time of year. It's no subspecies. Just a coloration thing. And it varies from wolf to wolf. Even the arctic subspecies of gray wolf can go through dark phases.

Maybe an Eastern Wolf?
http://djkb.deviantart.com/gallery/36590837
of Mackenzie Valley wolf