Re: Why does some hair get whiter, or greyer than other hair in older people?

The colour of hair, whether it is black, brown, or even grey, is the result 
of pigment cells in the hair root which gives hair its colour. As we all 
get older, these pigment cells and some other pigment enzymes (little 
things which make the colour) decreases. For some people, this decrease may 
occur at an early age. The main reason for this early graying is genetics. 
That is, for the majority of people, hair colour (and therefore, early 
graying) is inherited from their parents (or grandparents). Having said 
that, some diseases can also cause hair graying, but this is usually not 
very common.