Quite a bit of blue-screen was used for the Superman flying effects in the first film, in addition
to the ZOPTIC process (in fact they used just about every technique you can think of in one flying shot or another; they threw the kitchen sink at this movie in order to get it done). They tried to control for different shades of blue in a very narrow range, utilizing some color correction process, with mixed results. The most obvious example of blue-screen gone wrong in the original release prints was a shot of Superman flying past the camera and on toward Boulder Dam in the distance - Supe's suit came off as teal blue, almost green in this shot. It's been corrected in later versions of the film.
Applying the word "naturalistic"
to any aspect of Donner's Superman
is incorrect use of the term.