The Scott# 2943, Alice Paul issue is one that I find that still poses issues for people to identify. Sorting by color along can be error prone as there is variability in color and lighter inked versions which appear different in color. 2943 is easiest to separate by checking the tagging as it appears Solid. The 2943a & 2943b tend to be the more difficult since both appear as a Grainy Solid tagging. Using LW UV (black light) the three types can be easily separated. To help identify the differences and provide an identification guide I have added new images to the US Tagging & Luminescence Database.http://www.stampsmarter.com/feature...ingView.html
Below is an example of the new images. For each I have provided images taken under normal visible light (color variation), SW UV (tagged image) and LW UV (black light). I have also tried to show variations where appropriate. One item that threw me early on was Scott's comment that the 2943b glows bright pink under LW UV. All of the ones I have examined are bright orange under LW and quite unmistakable. Under SW UV the ink does appear pink so it may have to do with the light source used.
I will leave it to the reader to check out the other two images at stampsmarter.