Change in color of nose

Lately, I noticed that my 10-month old Shih Tzu's nose has some areas that are turning from black to a lighter color (sort of pinkish brown). Area affected is just under her right nostril up to her lips.  The areas are not extensive but I'm worried as to what might be causing this.

Aside from this lightening of a portion of her nose, she is her usual self.  After the hairball incident mentioned in my previous post, she is back to her normal ways.  She has good appetite, has been drinking water, her urine and poop are ok.  She loves to play.  She was also previously diagnosed with fungal infection of the skin and that was what was causing her to have brittle hair and itchy skin.  She was given an anti-fungal shampoo and although her hair still isn't as it used to be, she has been shedding less and itching less.  I switched her food from Royal Canin to Canidae recently.