Interesting. I did not know that there is this "diffusion" of the British spelling into the American spelling.
When I was in school in the former USSR, for whatever reason, our English teachers taught us only British spelling and grammar. I could not even imagine writing "labor" or "color" or "tumor" - it was always labour, colour, tumour. When I moved to the USA in 1990, it seemed to me that everyone except myself is misspelling words and also misusing grammar. I remember that I once started to argue with an American that it is incorrect to say and write "I have learned," because the correct way is "I have learnt."
And of course I was taught that people drive lorries (what's "trucks???"), eat sweets (what's "candy?
"), use lifts (what "elevators???"), RING each other on the phone, etc.