I think it’s futile to find the “correct colors” simply because there is no such thing. The colors in 1977 varied depending on what film stock it was printed on, the warmth of the projector bulb, the competence of the projectionist, etc. No two screenings would have looked the same.
Therefore I think it’s less important to try and match a specific reference, and more important to try and find what the colors were MEANT to look like, which you can only really do by looking at what color sets, props, actors, etc actually look like, then take into account factors like lighting on the set.
Another thing that can be done is to look at several references and look for what is similar between them. If you have ten references and seven of them say the wall is grey, two of them say it’s green, and one of them says its blue, then it’s probably best to lean toward grey.