I apologize if this comes across as insensitive, but I see nothing wrong with grey hair. Grey hair is a symbol of wisdom and I personally think it's quite attractive. I have to object to viewing it as a defect (yes, even at 18 - my sister had grey hairs at 18 after being raised on a TF diet.) I'm 35 and I have lots of grey hair, I'm pretty sure I'm not deficient in anything, and I *like* my hair.
It's a cosmetic issue, and it's only our youth-obsessed culture that has devalued *everything* about growing older that makes people not want grey hair. In many cultures, you weren't treated seriously until you started to go grey. Sometimes I think that's a more sensible way to go.
Embrace your hair. Grey hair is fabulous, I'm sure you're gorgeously grey. Don't buy the youth-is-great message. And I also think that looking for mineral/vitamin/nutrient deficiencies for all your perceived imperfections is probably not as productive as learning to live with them. Some of them. I mean, there's a balance, right? Grey hair isn't really on the same level as IBS or depression or something like that. Argh, this isn't coming out right. I'm not trying to trivialize your concerns, I'm trying to say that not everything has a nutritional "answer" and some things don't need one.