As you know, many mammalian species undergo seasonal molts (shedding and replacement of fur) which change their fur colors from brown to white. The snowshoe hare, Lepus americanus, typically undergoes the molt in late fall, which changes their fur color from brown to white. In the Pacific Northwest (Oregon, Washington), populations of snowshoe hares have been identified in which some individuals molt from brown to white in the fall, while other individuals molt from brown to brown. Provide a proximate explanation for this phenomenon.

Due to changing climatic condition, snowhare do not need further insulation and hence they change their fur coat color from brown to brown only.

Also, the risk of predation has reduced

Explanation:

The characteristics of seasonal color coat are observed in animals living in temperate and Polar Regions to protect themselves against the extreme climate.  

Mammals living in northern hemisphere, change their fur color from brown (in summer) to white (in winter) in order to camouflage against the snow. However, it is noticed that some snowshoe hare change their fur color form brown to brown again. This fact is yet not clear but there can be two postulates to explain this  

1.The brown coat snowshoe hare do not need further insulation  

2.These brown snowshoe hare are no more worried of predation risk which they generally reduce by changing fur color

helicase, i think thats it