Here’s a relevant quote from an interview around the time of the original release.
George Lucas said:
I visualized an extremely bizarre, Gregg Toland-like surreal look with strange over-exposed colors, a lot of shadows, a lot of hot areas.I’m not sure exactly what’s meant by “over-exposed colors” here though. It could refer to overall brightness: in digital terms, all channels over-exposed with blown-out highlights. Alternatively, it could mean over-saturated colour: one or two channels over-exposed, e.g. a shot that’s more or less monochrome red with solid bright red highlights.
Off the top of my head and from a look at 4K77’s thumbnails, I can’t think of any examples of the latter in the original Star Wars. So, I think this supports the idea some scenes were intended to be over-exposed.
EDIT: Just re-watched 4K77, and there are some shots in the garbage compactor and Tie fighters with some very saturated coloured lighting. Does anyone more familiar with film-making terminology know which of the above (or something else I haven’t considered) is the most likely meaning of “strange over-exposed colors”?
I think he meant high contrast. Gregg Toland did The Long Voyage Home, Citizen Kane, and Song of the South. I think it also refers to more natural lighting instead of traditonal studio lighting.