Isn't it funny that you buy a PC in UK with a UK keyboard and then when you type a letter, MS tells you - you can't spell ...... colour - color, harbour - harbor etc. etc.
It wouldn't be so bad, but English English was first, Computers originally needed a good hand from the English to actually work .......
Living and working in many different places I find that US Movies and Computers are spreading the american style of english so fast that English English is losing its battle...... even my own sons fall into americanisms sometimes - taught by UK schools !!!!!
What can you do ????? I install British English Spell Checker on all my office PC's, regardless of where I am, I use it in my writing ..... I try to pass it on as original english, but I would not want to be classed an old fuddy-duddy about it, I'm just proud of history and heritage / identity.
You can change the Spell Check preference to CUSTOM - British English, or later versions I think call it INTERNATIONAL ENGLISH ..... then you can safely forget Gates and his US spelling !
I always do that, but unfortunately the import of any document that has its language as US English over-rides my default, necessitating a change of default back to UK.
If you click on the menu-bar on <Tools> and then on <Language> on the drop-down menu, you'll find you can set the spell checker for something called English (British) and your problems will be at an end. Default is English (American)
Microsoft do many things badly but that isn't one of them.