The term box car red describes something that in real life encompassed a range of colours that depended on the mix of the paint. Railroads specified the percentages of each ingredient, based on preferences and cost.
The better pigments cost more, with the definition of better being longer lasting colour when the paint is exposed to sun light. The two classic ingredients were iron oxide red versus red lead.
So if I line up five boxcars, say from the Southern, Santa Fe, SP, UP and PRR, the colours should progress from brown, to rich red-brown, to (what we think of as) box car red, to oxide red, to orange oxide red. Well I don't have that exact combination, but I am able to show five box cars red demonstrate this range from cars painted in iron oxide red to those painted using red lead.
The brownest box car I have is this N&W PS-1 from Kadee.
With just a hint of red to it this AT&SF PS-1 from Kadee fills the next spot for a rich red brown car.
Falling into the mid point, the classic box car red, is this RI 50 foot SD from Proto 2000.
This C&NW PS-1 car from Kadee fits the bill for a oxide red freight car.
Finally, the classic orange oxide red of this PRR War Emergency gondola from The Tichy Train Group.
And just to make the comparisons in the same lighting all five freight cars in a line, which also demonstrates how we perceive colour changes according the light we view the colour in. In this case artificial light for the individual models, whereas the group shot is predominately daylight tinged with some background artificial light that was on in the room. Here I can't see the colour difference between the N&W and AT&SF freight cars, as they both look just brown to me at this distance. Close up I can see a difference.
Moral of this is that there is no one shade of box car red, and variety will therefore add realism to the freight car roster. What is of course just as interesting is each manufacturers interpretation of a railroads red and the variance between each, but I'll keep that for another time.