Re: What makes a cat's fur change color after a scrape or shaving?

Acquired depigmentation of previously normal skin and hair can result from 
many factors that destroy or depress melanocytes.  Thus trauma, burns, 
infection, and ionizing irradiation may have potent local effects.
Melanin is a dark pigment that is responsible for naturally occurring 
general and local pigmentation of the skin and, along with pheomelanin, for 
the color of hair. It is produced by cells called melanocytes.  Within the 
cells are small organilles or saccules whose sole task is the manufacture 
of pigment. 

I don't know why the hair color changes when animals are shaved.  I used to 
think this was a myth, but I did find conformation that it is true.  The 
hair coat usually comes in darker.  When the animal sheds and grows new 
hair it should return to the origonal color.  I could not find anything 
explaining why it occured.  In some breeds of cats, like the Simese, 
temperature has an effect on the hair coat.  Siamese cats living in warm 
climates have darker points than the same siamese living in a cold climate.

Reference: Small Animal Dermatology  Muller - Kirk - Scott
      Feline Medicine, First Edition  American Veterinary Publication, Inc.