I remember how people were conscious for the colour of their hairs specially at an old age when it turned white.  Where I had born and brought-up, old people use to apply, what we called it  "medhi".  That was the source of their head and beard looks turned red instead of white. At a latter stage different colours started pouring in with full marketing tools to attract old lad to looks young by colouring their hairs black rather then red by giving impression of its originality. 

Now there is good news for them, a scientific discovery why hairs turned white. As per Science Daily June 14, 2011: 

 "A new study by researchers at NYU Langone Medical Center has shown that, for the first time, Wnt signaling, already known to control many biological processes, between hair follicles and melanocyte stem cells can dictate hair pigmentation." 

"As per Dr. Ilto, the human body has many types of stem cells that have the potential to regenerate other organs,"  "The methods behind communication between stem cells of hair and color during hair replacement may give us important clues to regenerate complex organs containing many different types of cells."

Read full news in Science Daily