In some cases (not sure if this is too late for the OP’s time frame), they actually have done things like revisit the actual parts of France/Belgium where the original video was shot to get the actual foliage and soil colors correct.
That’s one thing they did in “They Shall Not Grow Old” among a whole bunch of others such as normalizing the frame rates of the hand-cranked films, etc…
The resulting restored footage is eerie in how contemporary it looks.