hair color/ skin pigment change

Question
my standard poodle has a strange patch on the back of his head. his hair is
almost gone and skin has darkened under this patch. what is this and what can i
do about it? the patch is much darker than his apricot/white hair and the texture
is different than his curly 11 year old hair.

Answer
Hello Debbie,
Sounds like your dog may have had an injury there or maybe a Hotspot.  When a dog gets a skin injury that damages the skin cells, the hair sometimes won't grow back and if it does it grows in a different color (typically in the original color the dog was as a puppy).  The skin itself will also take on a dark tinge.  When the new hair grows in, it is softer and more fluffy, like puppy hair rather than adult hair.  
Its almost like the skin injury causes the skin cells and hair follicles to "reboot" and start over as if the dog were a puppy.  As the dog ages, the skin and hair will go through changes, just like a puppy does from puppyhood to adulthood.  

I hope this helps you some.  If you have other questions for me, please feel free to ask.

Thanks for using AllExperts.com,
Kim