U.S. three-cent green postage stamps manufactured under governmental contracts with three different private bank note companies were studied concerning paper properties and ink composition. Stamp paper analyses revealed that each of the companies was using paper with different properties. Moreover, through the bending index measurement and calculation of population distribution of bending indices for each stamp manufacturer it was found that National BNC used two discrete types of paper, one with a bending index 85-115 GU/g reaching 52% of total tested samples, the other stiffer with a bending index 115-159 GU/g. The Continental BNC population (88%) had the bending index in the range 69-142 GU/g, the rest was within 142-192 GU/g bending index. Possibly three different papers were used by the American BNC within the first period (1879), one (20%) with bending index 66-89 GU/g, a second (52%) with bending index 89-113 GU/g, and a third (28%) with bending index in the range of 113-145 GU/g. The re-engraved issue (1881) was printed on two different papers, one (70% of population) with bending indices in the range 59-100 GU/g, and the other with bending indices in the range of 100-128 GU/g. "Green" as recognized by philatelists was found to be different for every manufacturer in terms of CIELAB values.