The upper plank is the "real deal" shade, common instead of white in earlier CIE days. The grey shade is standard for 9a0 the GSR period - for ALL goods and PW stock - and CIE up to the late 1950s. Light green started being replaced by white for logos and numerals probably in the early 50s, and "snails" were initially painted, as above. The stencilled "snails" were from the late 50s but became absolutely universal with some still to be seen well into the 70s when loose coupled goods ended.
FOR THE BENEFIT of anyone interested, I had a flick through several hundred photos purely on impulse yesterday (yes, in the winter season I really am that sad!), and looked at goods stock between 1972 and the end of loose coupled, late 70s. Roughly half, or perhaps slightly over half, of palvans and H vans were BROWN, the rest still (weathered) light grey. This would be relevant to many of the very excellent layouts we see which are based in this period.