One thing I failed to note earlier is the matter of the Emperor's makeup. As originally designed, it was meant to suggest extreme age, of such a span that it could only have been achieved through some unknown dark sorcery. The Emperor is described as "a Methuselah figure" who is "ancient, not old." In fact he's so old that he is beginning to evolve into something else--the ridge on his forehead is a point where his cranium is beginning to split in two. (And, unlike in ROTS, Ian McDiarmid was made bald up to the crown of his head, where the prosthetics stopped abruptly.)
The idea of the Emperor being so ancient and evil that he was becoming something beyond human was first suggested for ESB, where in the Leigh Brackett story conferences Lucas actually proposed that the Emperor should be immersed in a giant steel box, like the spice tank used by the mutant Guild Navigators in Dune. Still, it seems rather inconsistent with the idea of Palpatine as a Nixonian politician who came to power a scant few decades back--a point that would become obvious in the prequels.
The matter of "the Emperor's slugs"--the matte-black blob that in post-production was placed over one side of Palpatine's face during his closeups--is also addressed. Apparently this was due to another of the (myriad) failures of camerawork on-set--the lighting used caught the angles of the Emperor's prosthetic makeup in a rather distracting way and had to be adjusted by hand in post.
Another interesting anecdote about lighting involves the first day shooting on the Star Destroyer bridge: apparently Marquand wanted to use a rather dramatic lighting setup, with "red lights flashing and hitting the walls" as Kazanjian later put it. Lucas and Kazanjian both objected to this. Marquand said "It's atmosphere!" but Kazanjian said that it didn't match the look of the previous films. (Maybe it brought up bad memories of Irvin Kershner's style--and his meticulous concern for lighting that often set back the filming schedule?) In the end Kazanjian and Lucas got their way.