I’m just a hobbyist and these are my experiences…
Lucky me. I deal with black locomotives and freight cars, reddish-brownish freight cars, and olive-greenish passenger cars. So, color is easier in the 1935-1945 era.
But even reddish-brown freight car colors vary by road. To keep things simple, I like what Pat Wider did in Railway Prototype Cyclopedia Volume 3 (page 37). The colors are broken down into red(oxide), red-brown, and brown along with what roads used what and some paint formulas for AccuFlex, Accu-paint, Floquil, and Scalecoat (none of which are available to me). Here’s the listing filtered for the 1935-45 era:
RED (OXIDE): NdeM, SOU, T&P, UP, Wabash
RED BROWNS: ACL, ATSF (40’s), C&O (40’s), CB&Q, CG (40’s), CNW (40’s), DL&W, Erie (40’s), GM&N, GM&O, GTW, IC, ITC, L&N (40’S), KCS, L&N, NKP, NP, NYC, PM (40’S), RDG, RI, SAL, SP, SP&S, SSW, WLE, WP
BROWNS: ATSF (30’S), B&O, C&O (30’s), CRP, D&RGW, Erie (30’s), GN (30’s), MKT (30’s), MP (40’s)
Even though many roads are not listed, many of the main ones are, and although the periods are very general, this is good enough for me.
With my stock of Polly Scale paint running out, I decided to standardize on Tamiya XF paint. Vallejo was the other choice. Both are acrylic, very high quality and are readily available. Vallejo has many more colors and paint lines to choose from. Their paint comes in bottles that are shaken and dispensed through a tip which makes for accurate thinning or mixing – just count the drops.
But I find that too much choice is confusing, and I’d rather stir paint, so I went with the Tamiya XF line. I wanted only one brand to standardize on stocking of auxiliaries (thinners, retarders, etc.). Both of these lines are mainly geared towards the military modeller; the blacks, browns, tans, greys and greens are suitable for my era. The XF paint airbrushes excellently and overall, I feel this was a good decision.
But after standardizing on Tamiya, I found when it comes to freight car reds/browns Tamiya is limited. XF-69 NATO Brown is a good color. XF-9 Hull Red is very dark (but nice for O&W Cabooses). I have not tried their XF-64 Red Brown. Tamiya paint tends to have a lot of pigment. That means more vibrant colors. While I like XF-69, it is generally too rich in appearance for my tastes.
I turned to another brand of paint (so much for standardization) – AK Interactive Real Colors, a lacquer paint. Fortunately, this does not mean any additional auxiliaries as I already use lacquer thinner for cleaning my airbrush. I tested the following colors and this is what I have decided on:
RC066 Rotbraun for the oxide or “red” shade.
RC068 Rotbraun for the “brown” shade.
RC067 Rotbraun isn’t much different than RC066, but I mix 3 parts of it with 1 part RC068 Rotbraun to get the “red brown” shade. RC066 can be substituted. For easy mixing, I use a Tamiya 40ml mixing jar and dump the four 10ml jar colors into it.
AK paint is excellent quality (a real pleasure to airbrush) and is very much available locally.
For variation in tones, I can mix in RC026 No. 5 Earth Brown or RC065 Braun into the main color at the pre-weathering stage (prior to glossing for decals).