Canadian here, so "colour"! I also use "favourite" as a spelling, but when it comes to things like defense/defence I sort of flipflop between them. I generally don't mind what spelling other people use, but I do sometimes rag on people for fun if I know they usually spell it with a u but choose not to in a group chat or something.
sometimes i make a conscious decision to change color to colour/favorite to favourite when i'm editing documents or manually quoting someone or something. just because there's something funny and petty about it to me.
Another American reporting in with the "color" spelling. It's the standard here, and due to decades of social conditioning the u in the "colour" and other words feels extraneous on a personal level even though it's the original spelling. It's no big deal though.
I spell it as colour! Thats how I always grew up spelling it and seeing it spelled on various products. Like @Mistreil I also spell favourite with the u but I'm not loyal to spellings of any other words.
I live in the US and spell it "color" but I also tend to spell the color "gray/grey" as grey. No reason behind it, other than that I may have picked it up from my Scottish Mother and Grandparents.
The spelling/word pronunciation differences between US and UK English has always been interesting to me! I’m from Canada and use the US English spellings of most words, but I’ve always spelled “colour” with a “u”! “Color” just looks wrong to me, even though I know it’s not.
I’ve also always spelled “favourite”, “armour”, “flavour” etc with a “u”, but most other words I use the US spelling/pronunciation for, or alternate between US and UK English.
British English is standard in Australia, so I prefer to spell it "colour", and generally spell words using the British English spelling unless there might be a reason to use the US English spelling.
"color," i was friends with some british people online when i was younger and used to spell* "colour" but my freshman year english teacher tore me a new one for doing that in front of the entire gd class so i stopped. it's not the popular spelling in america, sure, but it was just what i was used to lol