This struck me today. Why would the BEP bother to create two distinct varieties of the 1902 National Currency and the 1914 Federal Reverse Notes? It had to serve some purpose. But examining the notes - I'm unable to find anything other than color that differentiates them. Does anyone have any insight as to why we had red and blue notes for those two series?
They moved away from the red seals I believe due to ink issues, the red faded and ran much worse than the blue. On large nationals, I prefer the look of the red. But some notes, like say the Tombstone, I prefer the blue look. Go figure.
On the 1902 Nationals there's actually a meaning to the change: they started using the blue seal in 1908 when they started printing the Date Back variety, with the "or other securities" clause. Of course, in 1916 when they switched to the Plain Back variety, they kept on using the blue seal--so the 1902 Plain Backs are, as the OP said, identical to the 1902 Red Seals except for the color. In some cases, the colors were chosen to make sorting of circulated notes easier. For example, when the first small-size notes were about to go into production, the plan was to use red seals for FRNs and green seals for USNs. But then someone realized that the green-seal USNs, when heavily circulated, might be hard to distinguish from blue-seal Silver Certificates. So they switched the colors for FRNs and USNs before production ever got started, so that the red-seal USNs would be easy to distinguish from the blue-seal SCs. (It didn't matter so much if the FRNs and SCs had similar colors, because FRNs are easy to identify by their black district seals, which don't appear on any other types.) But I'm not sure whether that kind of reasoning had anything to do with the 1914 FRN color change....
The Treasury changed from red to blue seals on 1914 FRNs because the red seals didn't wear well during circulation. The blue seals were more durable.
Now that I think about it, most large size red seals in lesser grade have faded or smeared seals and serial numbers. That may very well be the cause of the switch. If that's the case, I wonder if they changed ink formulas for the small size legal tenders?
