Welcome to HCM
You should know when melanin
fails to be synthesised in the hair matrix, the hair loses its colour. The loss of melanin may be temporary or permanent.There is some genetic predisposition
Diffuse greying may also be a sequel, often reversible, of acute febrile states, debilitating febrile illness, severe malnutrition
, endocrine dysfunction, malignant disease and severe emotional stress
There are some drug which can cause grey hairs common one is Chloroquine use.
Please see a Dermatologist
and if there is any cause is detected it can be treated.
Some nutritional supplement may give result if there is deficiency.
If no cause detected cosmetically have clean shave and use of ammonia free hair dye with due care may solve your problem.