Board Thread:Spoilers!/@comment-24323512-20131226023625/@comment-1826156-20140216002804

I figured Bae's reference to them being ruby slippers was more because he would be more familiar with the MGM movie than the books. Ruby Slippers are copyrighted so to stay safe they should keep them silver.

Disney did get away with it in Return to Oz though, there were rumors that they paid a hefty fee to use Ruby Slippers but that was later debunked. Wicked kept them silver but they turn red when enchanted.