divider sets the color of gray lines that divide items of lists.
listSelectorSDK21 sets the color of the ripple effect when you tap a list item. There was also listSelector variable that worked only on Android 4.4 and below and has been removed.
emptyListPlaceholder sets the color of placeholder text — the text that you see if there's no content — when you open an empty list. You can see it in Chat screen → Attach — Music if you don't have any music. If you do, you can move them from the Music folder for a moment and move them back after you're done.