One of our male cats (don't know age---he walked up and adopted us one day.)

He has developed some kind of skin condition, where he's losing hair ---it started around his neck and now seems to be spreading to his back and his face---the exposed skin looks pinkish.
Does nayone know what this is and the treatment?

Mange caused by mites. The vet knows the best treatment or you can ask at a pet store for what works with other pet owners.

Some people even put bacon fat on the mange to go away... an old-fashioned remedy, but I've seen it work.

Here's a link that discusses several causes of fur loss. I'm going to the main library page cause there's 2 parts that aren't linked. But it's the top 2 articles under "Bad Hair Days."
http://www.littlebigcat.com/index.php?action=library

One thing I would suggest... if it ends up being something for which your vet wants to do steroids, try to avoid it and find another solution. Also, if they think it's a food allergy, prescription foods are bad quality - you can do food allergy testing on your own, generally starting with no grain stuff.