You're right that his face was pretty clearly shown in the orginal ESB, albeit a bit darker than the present version as the abobe poster mentioned.

But there is definately a gradual reveal going on in Return of the Jedi. Since the two Emperors orginally looked vastly different (the first one being an old woman with monkey eyes I believe) that wasn't a problem back in 83. But now his scene in Empire ruins his introduction in Jedi. Therefore, the hologram should shroud his face more than it does now.