Unless you are just a “Collector”, colours should not be too much of an issue.
In real life, colours varied from one batch of paint to another. Colours faded, from the day they were first applied. Red was one of the colours that faded most noticeably. Not all cars in a fleet were painted on the same day, week or year.
If you have cars, that you actually operate out in sunlight; consider “Fading” as a natural act of nature, and one of the types of “Weathering” greatly sought after by some modellers in this hobby. I have a bunch of Aristo heavyweight passenger cars, in CN black, green, and gold paint, that have faded (Weathered) nicely, and look very close to how the cars in service actually looked, after a few years. CPR, maroon cars weathered nicely too…
Fred Mills