UPU colors

In 1896, Universal Postal Union (UPU) members agreed to standard stamp colors for international mail. This would allow faster processing of incoming mail. The standards set were:  File:GB half d centenary.jpg|Great Britain 1940 ½d stamp centenary commemorative File:GB 1d centenary A.webp File:GB 2.5d centenary A.webp File:Japan 1s UPU.jpg|Japan 1883 1 sen UPU definitive File:Japan 2s UPU.jpg File:Japan 5s UPU.jpg File:US 1c 1903.jpg|United States 1903 1c definitive File:US 2c 1903.jpg| File:US 5c 1903.jpg 
 * green for international basic printed matter
 * red for international post cards
 * blue for international first class mail

The US juggled their definitive stamp colors and became compliant in 1898. Japan did change its definitive and commemorative colors well in advance of the required change, but came up with a series that probably were not as most people would expect.

The system worked well for many years. However, as time passed and bicolor and multicolor stamps became the norm, the use of UPU colors was ended, guessed to be circa 1950. 



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