Comment by phire
The end result of a modern film "transfers" looks so good that people massively the amount of effort that went into the restoration.
The color has always faded. They have to color-grade it back to what they think it originally looked like, though it's more common to use artistic license what they it was originally intended to look like. Artistic interpretation always leaks in, and it will never match what someone saw in the theatre (and there was massive variation between prints even when they were brand new).
At least with TV shows like TNG, we have the tapes to use as a reasonably solid reference for what color was actually broadcast.
And then there is scratch and dust removal. They do so much in-painting to get the clean result that we associate with 35mm film today.
The color has always faded - well, not always. The gold standard for movie archiving is to store the movies color separated on three reels, one for red, green and blue, but not use color film, but a special black and white. There's no fading at all on these.
Sometimes the original negatives are in really good condition, but you still have to redo the color-grading, because the original color-grading was done chemically onto some transfer which now has faded or was just pretty bad to begin with, if you even can find it.