Stamps of the earlier eras were color coded. The United States first class postage rate stamps of the Nineteenth century were red-brown (the overseas stamps were blue). So were the first class postage stamps of Great Britain, Canada, and Austria. The reason had nothing to do with design or aesthetics. Red dyes were cheaper. Here’s why.
Inks are a combination of a coloring agent and a solvent to move that coloring agent onto the medium that it is printing. Coloring agents can be either organic or inorganic. Inorganic pigments are expensive and often change color over time. The earliest stamp printings were in the hundreds of millions, and the postal authorities expected the plates that these stamps were printed from to be used over again over many years while the stamps were in use. They needed a cheap, commercially available ink that could be reordered in quantity and which would be pretty much the same exact shade over the many years that the stamps were being printed.
Red dyes were among the first pigments that humans created. The reason was simple. Oxygen and iron, the two components of red dies, are the first and fourth most common elements in the earth’s crust (the second and third elements