It's just another example of simplified spelling commonly taught in the US. I don't know how far it goes back but I'm sure it pre-dates WWII (1940).
It doesn't matter whether you use British or American spelling, what matters is you are consistent. So don't type "the colour of sulfur is usually yellow". If you were writing a College paper in Canada, you get demerits for inconsistency within the document; you can however use either British or American English spelling for full credit provided you stay with one or the other throughout.
The observant will notice I use British spelling, which is what was taught in Canadian public (pre-secondary) schools until the early 1980's. That is when computer spelling dictionaries tended to be tied to the keyboard layout in the computer's OS configuration and for a very long time only the US layout was available for English speaking persons, something that most US readers are probably unaware.
For Post-Secondary (College) essays, either was allowable for quite some time, at least since the 1960's and I suspect anytime after WWII, as long as you don't switch between them within the document.
The English we speak was significantly influenced by the French language so it's hardly surprising to see some Gallic influence in the language. For many years French was the official language of the UK; English was only spoken by the common, unenfranchised masses.