If I look at any number of color pictures, the cars appear to be some widely varying browns. However if I watch volume 3 of the NRM Film Collection (the Kim Bird one), they appear predominantly some sort of red which appears to have faded to almost a purple. This appears to be quite different to the brownish red Allambi is now wearing in the NRM which I've gathered from the other threads is a pretty good match for brand new 'Regal Red' which the Suburban cars were also painted. Allambi also appears much redder than any picture of a Red Hen that I've seen.
Am I just seeing a change in the color that was used over the years, a difference in red balancing or some just the fading of a red that was a red and green mix, which as the weaker red pigment fades may become more brown? Or were the Suburbans just not painted 'Regal Red' and I'm down a rabbit hole?
I've tried mixing some of the color mixes I've found around the place (although I've used Pollyscale rather than Floquil); a 50:50 mix of Pollyscale Caboose Red and Boxcar red seems a pretty close match for a reddish brown under 5000k light with Oxide red for light fading and then progressively adding a light cream to the Oxide Red for a really faded (almost pink primer) look.
Reddish Brown: http://comrails.com/pic_cd/cd_p0109180.html
Faded example: http://comrails.com/pic_cd/cd_p0104226.html
Out of curiosity I ordered the Humbrol colors recommended in the modelling notes for the centenary baggage cars and 800s; a 5:4:1 mix of 9 Tan:19 Bright Red: 14 French Blue. As might be expected, it's a pretty strong red with only a hint of brown; far redder than the above pictures.