I spell things mostly the traditional way. Colour, favourite, realise, organise, mum etc. To me, some American spellings just look weird (eg. spelling defence as defense and grey as gray).
I'd like to point out:
Metre is a unit of measurement while meter is a device used for measuring something, for example, "I ran a couple of metres so I could see what the reading was on the electricity meter".
Same goes for centre and center. Centre is a gathering place (for example, a Pokémon Centre) while center is the middle of something. "I went to stand in the center of the Pokémon Centre."
I think most people don't really care about the difference, but I'm just throwing it out there.