not much that you can do about the collar. it is discolored due to sweat, hair tonic, and body oils absorbed over the years. many collars that are darkened like yours tend to crack and rot out at the fold if they have not been stored and tended well. if the disoloration really bugs ya, you might try some detergent rubbed in and dabbed off. the next possibility is nail polish remover, or acetone on a q-tip, and rub it on an area. you will remove some of the discoloration, but since it is deep in the leather, there will always be some discoloration.