Stamps with code colors green, red & blue

In the first half of the last century, it was common practice to affix stamps of a fixed color to mail items for international mail. This had its advantages: manual sorting was accelerated, and it was easier for foreign postal officials to determine whether a mail item bore the correct postage. Thank you Following my fall from my bike, I received a new femoral head, which means I will be somewhat less mobile for the coming months — as a 'walker-stamp blog contributor'. I would like to thank blog readers Willem Hogendoorn, Randy Koo, and Guido heartily for their encouraging comments. Indeed: I am quite bruised, although that remains invisible to myself. Collaboration between author and stamp blog reader The reactions to my fall from my bicycle and the subsequent hip fracture reminded me of my stamp blog period from 2003 to 2015. Back then, multiple comments came in after almost every article, often containing interesting additions, corrections, and further insights. There was a close and lively exchange between authors and readers. That contrast with today struck me once again, even though a valuable philatelic addition was posted by a reader just a few months ago. Over the years, the number of authors and readers with extensive philatelic knowledge has understandably declined—partly due to death. At the same time, I expect and hope that new readers with a solid background have also joined. This raises curious questions for me: what causes so few comments to appear on articles these days? What philatelic knowledge exists among the current readers? And who still possesses reference works that can supplement or enrich insights? Added value and addition In my response to the article 'Naarden Turns Blue' of January 23, I already mentioned that relevant philatelic background information exists regarding the use of the color blue on stamps. Randy Koo's article focused primarily on visual material, which is valuable in itself. From a philatelic perspective, however, additional context can sometimes provide extra depth. Therefore, hereby, as a supplement, is some information regarding the functional use of the color blue in international postal traffic at the beginning of the twentieth century. Color codes in international postal traffic At the end of the 19th century, the Universal Postal Union (UPU) used color codes for international mail to simplify and speed up manual sorting. Thanks to these colors, postal employees—even outside the Netherlands—could quickly determine whether a postal item was correctly and sufficiently franked, regardless of the currency used: – Green for printed matter to foreign countries, marked 'Postage Paid / Port Payé' or a stamp with 'PRINTED MATTER', usually for impersonal or business mail. Red for personal postcards abroad. Blue for personal letters abroad. Consequences of the Second World War I do not know why a switch from red to green occurred in printed matter and personal postcards in some years. Whether such color changes also occurred in other countries remains an open question for the time being. After the Second World War, these color pairings were gradually abandoned in most countries. However, the use of blue for international letter mail remained remarkably consistent in the Netherlands and was even applied until 1953. Slot Just like in previous years of blogging, I warmly invite readers to share their knowledge, experiences, or reference works. A comment can deepen an article — and keep the conversation alive.