Doug and Keith, and all:
Tim Schreiner found the picture that I referenced above that I said was, in my opinion, the exception to "the rule".
This photo is probably taken around the same time as the picture Doug posted, showing the oil burning #70 and in the distance a caboose with a very black looking roof.
As you study this photo, you will see quite a bit of oil residue, but the cupola roof is absolutely black roofing material. The egdes of the roof over the facia appear to be painted, with residue, but it is likely that the roof is also black like the cupola.
Note too, that the pedestals and brake cylinder have been painted black.
Finally, note the chalked date of "9.21.39" on the body, so this photo is close to 1940. I believe it was said to have been taken in Idaho Springs.
I remain solid that in the days prior to abandonment in April 1937, cabooses were not painted this way. But in 1939, at least #1003 was.
Thanks, Tim, for coming through with this great photo, undoubtably taken by Kindig. Wish we had more color photos!