Faded prints and typical home video overbrightening account for pretty much all of the differences. There was also likely a missing filter on home video releases regarding the R2 canyon scene.
Basically the color of crap film stock goes all to hell over ten years, let alone twenty years. It's only because of superior-quality Technicolor prints that we actually know how things looked back then (more or less). We do not have references of that quality for Empire...