In 1898, the UPU required that the postage stamps representing typical Union rates be printed in blue for letters, red for postcards, green for printed matter. In 1898, the US rates were 5, 2,and 1 cents respectively. In 1925, the card rate was raised to 3 cents. In 1932, the printed matter rate was raised to 1.5 cents, yet the 1 and 2 cent stamps were maintained in green and red through the 1952 end of the color rule and beyond. Does anyone know (presumably from something published between 1925 and the present) the reason why the US did not change colors when the rates were changed.?
Canada does appear to have changed colours with the rates.
1903 Edward VII
1c green printed matter, 2c carmine postcard , 5c blue letter.
1949 George VI 1c remains green printed matter (--) 3c changed to violet 4c now carmine postcard (+1c) 5c remains blue letter (--)
1953 issue 1c reverts to brown 2c becomes green printed matter (+1c) 3c reverts to carmine postcard (-1c) 4c becomes violet 5c remains blue Letter (--)
In 1898 the UPU issued rules to standardize the color of stamps for certain basic rates so postal clerks in any country could tell if a the postage on a letter was properly paid. The colors were green for a domestic post card, red for the first weight unit of a domestic letter (in the U.S., the first ounce), and blue for the first weight unit of an international letter. The rule was issued in 1898, forcing the U.S. to change the colors of several of its current definitives (see Scott 279 and following). Red remained the color of a basic U.S. domestic letter rate stamp until 1933, when the rate went to 3 cents and the Post Office entered its "Purple Period." Without digging out all sorts of other reference books, I couldn't say why red did not become the color of the new 3-cent stamps.
In the old days, postal clerks around the world were not too knowledgeble about the currencies of the various countries. To ensure that letters were properly prepaid, the UPU made up rules that covered the colour of stamps.
Thus the stamp paying the basic rate for a letter would be red. Hence the US 2c stamp was red as was the UK 1d stamp, the Canadian 2c and later 3c stamps and the Australian (and other British Empire countries) 1d stamps. Thus postal clerks abroad knew that the proper letter rate was paid.
" Statutes of the UPU Convention of June 15, 1897, effective on January 1, 1899, required that postage stamps representing the typical Union rates or their equivalent in the money of each country to be printed as far as it was possible in the following colors: stamps of the value of 25 centimes in dark blue, stamps of the value of 10 centimes in red, and those of the value of 5 centimes in green."
Above from from Wawrukiewicz and Beecher's "U.S. International Postal Rates, 1872-1196", page 3.