In what ways has the wolves changed in the book? Why?

Which wolves are you referring to? Is it Buck?

I see what you mean. After some years, the wolves of the valley are seen to have splashes of brown and white. Yeehats speak of a Ghost Dog that haunts the woods and slays the bravest hunter. One wolf returns to the valley each year. He sits and muses, remembering, howls once and then rejoins his pack.