The steps were silver like the other hardware. White may have been used at some point, but it would have been the exception, and not the rule. I have heard that there may have been white trim on locomotives and cabooses in WW2 due to shortages of aluminum paint. If this were true (and I have my doubts), I don't think it was widespread. At the end (1968), some cabooses had their roofs painted silver, over the black tarpaper. As for the underframes, I remember looking at a few cabooses in the late sixties and early seventies and the wood parts underneath(frames, floorboards, etc.) do not appear to be painted but looked to be weathered wood. The brake cylinder and trucks (and maybe other metal parts) looked to be painted under the years of grime. The interior was painted a "pea green". I seem to remember that it was not a really bright pea green and may have been on the lighter side. It may have been the same green paint used in the locomotive cabs. It was also trimmed in black. I am going to have to dig out some old slides that I took way back when, to confirm all of this.