are we going away from the original post which was looking at words and not accents? because if we are talking accents there is no one single british or American accent anyway.
Innit!
Geordie being the best accent!
Mirch, you are talking about two different things in your initial post, your first example is of spelling differences, second and third are based on different names for things.
A flat is the same as an apartment, just 2 different words.
Colour is the correct spelling of the word.