I've got a book here from Germany in the 1990s which contains the history of Agfa from Rodinal up to then and gives examples of a color plate they were selling to the public in 1916 and the colors still look beautiful. That's why the K14 process is a slight variation which Agfa (just to use 1 name & make it easier) had developed.
If color was invented in USA in the 1930s, then why are there color photos (not hand colored, but actual color negatives) from Germany as early as the mid-late '20s? I'll look for the book and give you the ISBN so you can see for yourself.
And PE, history is always written by the victors.
Yes, additive color plates (Lumiere Autochrome) were available well before WW1, with variations by other manufacturers including Agfa. The theory of the process was suggested by Young in 1807(!), and proved experimentally by Clarke Maxwell (U.K.) in 1855, with a color photograph of a tartan ribbon.
Subtractive color photography is a different system altogether, using a triple-layer film, and Kodachrome and the 1930's Agfa had that in common.
The point is that neither have any similarity with the earlier additive Agfa, and each of then has a totally different approach to the chemistry of the process.
PE could explain it much better than I, but basically Agfa put the colour couplers in the emulsion, Kodachrome has them in the developers (three separate developers for the three colors). (Both remarkable achievements, and I have read that German organic chemists were second-to-none in the
19th and early 20th century.)
All E-6 films now have couplers in the emulsion, which is why Kodachrome and K-14 are sadly at risk of becoming history.
So we can agree that history is (sometimes) written by the winners, and that color was not invented in the US....but that the laws of physics and chemistry take no regard of politics or countries.