If I am correct, Theatre Mode currently does not have the option for the 'next' button to be displayed in a different colour when pressing it won't result in anything. (e.g. when it's only a single track being played, or when the last song in a playlist is playing)
The 'next' button will always indicate/suggest it can be pressed anyway.
So this is a request to add a 'next disabled' feature to the Theater Mode.
(or prove me wrong in pointing out this can already be done)