US Proprietary Stamp RB4 V. 2013 Scott Specialized Catalog

I think I have this stamp correctly identified as a Scott RB4 as listed in the Proprietary Stamps section of the Scott Specialized Catalog:



Here's the problem: I'm using a 2013 Scott Specialized Catalog and the illustration for the stamp is supposed to be design RB1a, but the catalog listing suggests the Scott RB4 is design RB1 (not RB1a). I checked an older catalog and it would seem that design RB1a is correct, even though it is not listed that way in the 2013 Scott Specialized. Could this be a catalog typo?

Assuming this is a Scott RB4, is the stamp shown above considered to be on violet paper or green paper?

There is no such thing as an RB4. RB4a would be on violet paper and RB4b would be on green paper. Your picture implies that it is green paper, but determining color on these based on web images is virtually impossible as the differences can be subtle. When you look at a violet and green side by side the difference is apparent.

(Although the so-called "intermediate shade" which looks somewhat green on its own but is classified as a violet paper, is a real pain in the keester.)

The true green paper is a very vivid shade.

Thanks. At least you confirmed my identification of the stamp (at least as well as could be expected through a scan). I was leaning toward the green paper (RB4b) variety also.

I guess the 2013 Scott Specialized catalog was in error when it incorrectly noted the stamp illustration as an RB1 v. the correct RB1a design as shown in earlier catalogs. (I wonder if it was corrected in later editions?)

All but guaranteed that this is violet paper. Green paper is really green, and would show up even in a scan.

Now I'm really confused ... these revenue stamps are really a challenge to correctly identify.

They are not that difficult once you have seen a violet paper and a green paper together at the same time. Then the difference becomes very obvious. The "intermediate" paper is usually a pale violet with a greenish cast; again direct comparison will make it obvious that it is not green.
Remember we are dealing with a paper that is 140 years old, plus the idea of quality control in any modern form did not exist. And it was not a particularly well made paper to begin with. The dyes for the paper might have been obtained from more than one vendor or added by more than one person during (pre-electric light) manufacture so there are always variables to how it turned out.