Semi piebald.....possibility...
I have seen same thing in blacktail and elk....
Some do change like we do....grey hairs...
The old Roosevelt of the Oregon coast used to be much larger animals and older animals used to turn more of a grey color phase....nicknamed the greyghost(much like the clues deer which is usually this color i am told)....
But when you see one of the old bloodline...they are huge in comparison to others.....once saw a cow that had ro have tipped the scales close to 1000#....made the broncoII we were driving in look to small to pack it out of the woods.....
A four point bull i was trying to kill one bow season was killed by a rifle hunter late season 20 miles away....the tractor that they packed it out of the field..fully extended bucket with the elk head chained to the bucket..feet still touched the ground........giant....and the old boy I knew that killed it passed away not too long afterwards......felt honorable not taking that bull...and ol' Bill got him......