A while ago I wrote in with this question – Pea-Sized Bald Spot on Crown with Small Hairs in the Center
After visiting my doctor it turned out to be alopecia areata that was triggered by workplace stress I was going through at the time. The stress was relieved and the area grew back within a month.
My next question is unrelated though – when you look at a hair that has been shed, is there any difference between a white hair bulb and a dark hair bulb?
In my humble opinion, alopecia areata is an auto-immune issue where your body attacks its own hair follicles (to put it simply) and it has been occasionally linked to stress as a precipitating factor. It may have been a triggering factor. Hair loss from alopecia areata often will grow back with time (with or without any intervention), but it may come unexpectedly at any time in the future.
Finally, there is no difference between white and black hair bulbs.