Hi, pick,
First, keep this in mind, here in the US each state is in charge of their own local roads, and going back far enough there were only limited national standards - the states set their own standards - 50 different “versions”.
So, typically in the 50’s and before, you would find considerable variation from state to state. BUT, yellow center lines, sometimes single, sometimes double, sometimes broken to allow passing, go back at least to the 40’s and likely before. Some states did use white center lines and that could be seen into the 60’s or later in rural areas.
In the last 30-40 years the double yellow line seperating traffic of opposing direction has gradually become completely universal. White lines are now used only to seperate traffic lanes for the same direction of travel - and we have a lot multi lane highways.
Another important point about older markings, before the 70’s or 80’s it was not common to see the outside edges marked with lines of any color. Rural road or big highways, it was simply not done back then. When that did start happening it was only on high speed, major highways at first. It has only been in recent times that marking the shoulder edges of almost all roads became norm.
Another important note - to this day, a great many residential streets, city, suburban or rural, still have no lines at all, no center line, no edges, no nothing.
So without specific data from a specific region, yellow or white for older eras, two lines or one, without shoulder lines, will look believable for the eras you have mentioned. And leaving smaller local roads completely unmarked will also look very correct.
Sheldon