Invasion?

I have brown hair. But a lot of my friends have black hair and around their mid-20s, or even earlier, they started to find white hairs on their head. I'm not rude or anything but every once in a while I would give them a gentle ribbing about it, specifically my boyfriend who has a TON of random white hairs nested in a small area just above the right side of his frontal lobe. Well, though I am yet to find nary a grey or white strand on my head, I found this little present today. A white hair in my eyebrow.

IS THIS NORMAL?? I am thinking it's probably because my eyebrows are black. But I haven't seen this phenomenon on any of my prematurely white-haired friends. Are my eyebrows going to turn salt and pepper while my hair stays a solid brown?  Is this a random incident or is this hair merely a scout, paving the way for the rest of them. I need answers. Anybody?