Greying of hair is a normal aging process which starts around 30 as the melanocytes activity of the body slows down and gradually the melanin production in hair stops. If it is happening before this age, it is called premature greying. This can be genetic and also due to deficiency of essential vitamins and minerals.  You can delay the process of greying of hair by some lifestyle modifications. Take adequate sleep and drink lots of water, eat lots of fruits and green leafy vegetables. Few tablets can also be prescribed for the same. there is also one lotion which is supposed to work. You can call me or contact me using online consult option with photos for detailed​ prescription.,

It may be vitiligo but without seeing your problem i cant tell the exact diagnosis. I think you should consult a nearby dermatologist for proper diagnosis and treatment first.