I have a copy of RH White's Encyclopedia, and he has an interesting write-up on this stamp. This is copied from Volume III, page 15 and doesn't really refute the idea that there was some sort of chemical attack. In fact, none of the pictures in the Encyclopedia are even close to a blue shade, though one version of 273 is called "bluish-green".
Posted 08/21/2016 7:48 pm
