Ok, I found the answer on the first question:

In the case of sun-induced bleaching of eumelanic (dark) black hair, hydrogen peroxide and superoxides (free radicals) induced by the UV component of sunlight,act to disrupt the melanin "granules" eventually to a degree where the products of disruption are no longer black. That lightens the shade of hair color. The hair is dead tissue, so those melanin granules, once bleached, cannot be replaced.
Unlike hair, the skin is alive, The melanocytes of the epidermis are stimulated to produce greater numbers of melanin "granules" (melanosomes that actually are much more complicated than granules). The melanosomes are transferred in increased numbers from the melanocytes to keratinocytes of the epidermis causing the darkening (tanning) of the skin.

The persistent darkness of sunburned ski, results from an inflammatory response (reddening )induced by UV light. It is a complicated process which ultimately results in the destruction of damaged components of the skin and their replacement. Various agents that produce the inflammation as well as growth factors produced by keratinocytes, act on melanocytes,as repair processes go on, to produce more melanin "granules" darkening the repaired epidermis. The elevation of melanin production may keep the skin dark for long periods following "healing" because the stimulating agents remain elevated for long periods.



>Hi everybody,
>
>Ok, that I just got from my manager. Assuming I actually have to answer these questions, I have absolutely no clue. Let's be as serious as we can.
>
>===================================================
>Happy Halloween! The erudite and secretive Editorial Board of the
>Thought for the Day celebrates this auspicious holiday in an untraditional way
>--
>not by trick-or-treating -- but by posing a pop-quiz! So sit down, and
>do not cheat by copying answers from your neighbors answer sheet. These
>questions are seemingly simple, but do not be fooled: No one has ever
>satisfactorily answered any of them! But fear not: Grading will be on
>a curve.
>
>
>
>Why does the sun lighten our hair, but darken our skin?
>
>Why can't women put on mascara with their mouth closed?
>
>Why doesn't glue stick to the inside of the bottle?
>
>Why don't you ever see the headline "Psychic Wins Lottery"?
>
>Why is "abbreviated" such a long word?
>
>Why is it that doctors call what they do "practice"?
>
>Why is it that rain drops but snow falls?
>
>Why is it that when you're driving and looking for an address, you turn
>down the volume on the radio?
>
>Why is the third hand on the watch called second hand?
>
>Why is the time of day with the slowest traffic called rush hour?
>
>Why isn't there mouse-flavored cat food?
>
>You know that little indestructible black box that is used on planes?
>Why can't they make the whole plane out of the same substance?