Ridecamp: [RC] white hair/saddle fit

I know there was a discussion a couple of months ago about saddle fit and 
white hairs showing up after shedding out, but don't recall anyone mentioning 
how soon white hair can show up.  Posting for a riding buddy who purchased a 
beautiful barely broken-in OF at the convention in March. She had been riding 
her 16'1 Bey Oro son in a Big Horn prior. OF seems to fit him great, and no 
soreness in the back after multiple checks. However has within the past 3 
weeks found sparse patches of white hairs intermingled amid the bay on both 
sides of the back toward the loin area.  Would these be showing up this soon 
from the OF, or are they now showing up from the Big Horn? 
Recommendations/advice would be greatly appreciated.

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