Hi, I have done my reading from my Scott's catalogue and the books by Friedberg and by Castenholz. However I am still very confused about the difference between the b and a stamps, that is violet vs green paper. Any guidance or links would be most appreciated. Thank you.
Violet paper has a black vignette. Green paper has a sepia vignette, despite what the catalog says. Also the green paper vignette tends to leave a slight ring on the reverse. Otherwise, looking under a UV is really the only way to be sure, since intermediate paper looks greenish, but shows up violet under UV.