Codec 16 uses the room palette, from the little I've looked at it. It accesses a palette redirection table which is also accessed in some cases by codec 1. The redirection table it created at runtime, and is only modified by two script commands (kludge commands for those who know what those are about, it's not really essential knowledge to get this) - build-palette-shadow and set-palette-shadow. My guess is, in the cases where the redirection table (which redirects costume palette entries to room palette entries) isn't used, the palette of the room is used. Haven't looked more at it. This was found in the CMI code, however, The Dig and FT should be the same.