I've seen one in the fall that was a greyish/white on the back, had a calf of normal colour. In the spring it can be from ticks, bald spots, sometimes some huge bald spots result from them rubbing off ticks. Results in a lot of spring die offs as they have no coat left to protect them from the elements. Had one here in northern Alberta about 10-12 yrs ago. It kicked the krap out of the moose in a pretty large area up there.