The White Border Era refers to postcards published 1915-1930. Not only did German publishers produce most postcards before World War I, the German group IG Farben held patents for most colorants and dyes. Postcards with a border saved ink, and did not have to be cut precisely.
Here we have a 1924 aerial real photo postcard and its white border color version, published by Hermann Post Card Co., Chicago.
The real photo postcard is printed on AZO paper.
The white border card uses lithography, with a black halftone key plate. Hermann Post Card's colorist painted out the baseball field, and guessed at some other things.