Strange pink spot on horse's muzzle

[MsSteno]

Has anyone ever seen or heard about pink spots developing on horses or their muzzles? My Dun colored Kiger mare has a dime sized pink spot on the side of her muzzle that I thought was a scrape but upon closer inspection, the skin is completely intact and smooth.:confused:
My friend thought that she heard that these can be caused by a vitamin or mineral deficiency but she can't recall the details. I have searched and searched to no avail so any advise or direction would be greatly appreciated.:)

[Pancakes]

Sounds like vitiligo.

http://www.thehorse.com/ViewArticle.aspx?ID=4324

[jaimebaker]

Can also be a copper deficiency.

[LarissaL]

My tobiano Arab/Saddlebred developed some flat, pale spots on his muzzle and mouth about two months ago. I believe his was related to wetness and muzzling to reduce grass intake. He moved to a new farm and had the muzzle pulled and I've had no recurrance.

http://www.facebook.com/photo.php?pid=7082800&l=2e414ee499&id=739530133

Also a question for those that know vitiligo, in humans isn't that an autoimmune issue? I googled briefly when the above popped up on my guy and I never saw reference to autoimmune in horses affected with vitiligo.