Inside ear flap pigment changes

Question
Since June the skin on the inside ear flaps on both ears of my 4 year old schnauzer poodle mix, have begun to turn black.  He shakes his head and scratches his ears frequently.  I have taken him for 4 vet visits (to two different vets).  They say his ears are definitely not infected.  
Have you ever seen the inside of ear flaps change color in a dog of this age?  If this was your dog what would you do next?  Is it worth a visit to a veterinary medical school (Univ of PA)?
I welcome your suggestions.

Answer
Generally, when one sees black spots on a dog's belly, it is due to a fungal infection. I would think this could be a similar thing, although I have never seen ears like that.

Make sure that his ears are TOTALLY clear of dirt, wax, and HAIR. He is scratching because something itches. It could be a wad of dirt or wax way down in his ear, or it could be a couple of hairs rubbing together as they meet at the opening of his ear canal.

Try scraping at the black stuff with a fingernail and see if any of it comes off. You might also try rubbing at it with a bit of Listerine and see if that helps, although it may take a few applications of the Listerine to see results if this is indeed a fungus.