Armand,

Personally, I use the term "boxcar red" as a generic term referring to
"some shade of tuscan/red oxide/reddish brown/brownish red/whatever".

I used to think that there was some 'correct/accurate' color for any
particular car painted at a particular time and for a target modeled date.
The more color photos of freight cars I look at/study for color - the more
convinced I am that even two cars which were painted on the same day out of
the same batch of paint ... will have differences in color in just a few
years. Please note that I am not talking about differences in the color
image (photo) but rather the fact that you see a difference from car to car
when you see two cars in the same photo that are from the same RR and
number series.

My current approach is to not pay attention to the actual shade of any
particular car as much as to the "general shade" for a particular RR.
And, most importantly, to try to achieve subtle variations that are in
the range of "there if you look for it" rather than "immediately noticeable".
Yes, I start with a different shade of paint for a Pennsy car than I do
for an RR that had "more brown" to their paint than the "more red" of Pennsy.
But every time I do another Pennsy car - even if it is from the same car
series and target modeled date - I vary the shade.
The primary way I vary the shade is by using an "oh so slightly different"
mix of the base paint. But I also use different shades of weathering colors
(and weathering amounts). Another way of saying this is that I don't pay
a lot of attention to actual paint mix formulas for "box car red" and use
them as a "starting point". Of course I try to get the 'range' "correct"
for the particular car ... but it is of zero importance to me whether
this car is precisely the same shade as some prior car ... in fact, when
painting freight cars "box car red" I like to use Maurice Chevalier's
axiom "Vive La Difference!".

With respect to "box car red" my overall goal is to have a train/yard that
looks "every where similar" and "every where different" ... at the -same- time!
It works for me. YMMV.
- Jim in San Jose