Help! My Hanks nose is turning from black to pink.

Question
I'm the proud mom of two wonderful boxers, one of whom we just rescued three weeks ago. He's a flashy fawn with a full black muzzle. Last week his lips turned red on each side under the nostrils. The area has gone from black to light pink and is spreading. I'm completely baffled why he's losing pigment this way, and can't seem to find any real answers via the internet. He eats out of stainless steel and I feed raw so it's not a food allergy to corn, gluten or grain.
He also just had an extensive blood panel that came back perfect. He's happy and it doesn't seem to be bothering him. I'd appreciate anyone's input! Thanks!

Answer
It could be discoid lupus:

http://www.veterinarypartner.com/Content.plx?A=2470

http://josiefinch.hubpages.com/hub/How-To-Treat-A-Dog-with-Discoid-Lupus

http://www.highplainsvet.com/ask-the-vet/discoid-lupus

http://www.skinvetclinic.com/pdfs/discoidlupuserythematosus.pdf

http://www.dogster.com/lifestyle/how-to-deal-with-discoid-lupus-in-dogs

http://www.peteducation.com/article.cfm?c=2+2111&aid=425

Read these articles and see if it applies in your situation, then talk with your vet.

Good luck and hoping it improves.