Mini Schnauzer skin lesion

Question
Hi. My alt and pepper schnauzer, Juliette, is 9 years old. She has always chewed on her paws (my vet said she had some skin allergies)so they have turned a reddish burgundy color.
Today I noticed a patch of fur on the front of her right front leg had turned the reddish color - in the middle of her leg so I looked and there is a black sore underneath the red patch of fur.
It's about the size of a dime and it is slightly raised and rough.
I am wondering if the sore is there because she has been chewing that patch or if it is something more serious and she is chewing it because it hurts or itches.
Thank you.

Answer
There is a pigment in dog saliva that turns the hair a rust color when they lick.  If she is licking her paws, the paws will turn colors.  If she is licking a sore, it will do the same thing.  This could be a tumor on the skin that she is trying to get to.  Have the vet shave the area on  the leg to see what is under the discolored hair.