Greying of hair is a normal aging process which starts around 30 years of age. If happening before this age, it is called premature greying. The hairs which have already turned white cannot be turned back to black. But 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 multivitamin tablets can also be prescribed for the same. there is also one lotion which is supposed to work. You can contact me with photos for detailed​ prescription. ,