Anna Hoad and Erin asked:
How can hair change colour along its length? Why also does it change colour with age and eventually go grey?
Your hair is coloured because you have cells that pump pigment into the hair as itís growing. As you get older, these pigment cells basically get a bit knackered and they stop putting colour into your hair - which is why your hair goes grey. It doesnít actually go grey, in fact, it goes colourless. It goes white, but against the background of darker hair, it may look gray. This is because the pigment has stopped being pumped into the hair.
Also, pigment cells don't continually pump pigment into the hair. They may take little breaks, going in a cyclical way, and so itís perfectly possible for hairs to be different colours along their lengths. Itís probably unusual that youíd have zebra print hair, but it is certainly possible that they might stop producing pigment for a bit and then start producing pigment again.
Anna Hoad asked the Naked Scientists: Dear Chris I searched through your wonderful website but couldn't find an answer to this: My hair is naturally black, undyed and long enough for me to observe changes in the colour. Some of my hairs are colourless for several inches at the ends for but appear to have regained their black colour towards the root. How can this happen? Anna Hoad What do you think? Anna Hoad, Tue, 9th Mar 2010
Hair growth and pigmentation is cyclic, not continuous ...