I write 'colour' most of the time. But when I comment on US websites, I use 'color'.
I suppose that's a case of 'When in Rome ....'.
Still, there are some words whose meaning changes completely whether you use US or British spelling. In British English, the US-spelling 'pedophile' becomes British-spelling 'paedophile'. But British-word 'pedophile' means 'somebody who loves feet' (a foot-fetishist), from the same Greek root as 'pedal','pedestrian','centipede', etc.
I suppose that's a case of 'When in Rome ....'.
Still, there are some words whose meaning changes completely whether you use US or British spelling. In British English, the US-spelling 'pedophile' becomes British-spelling 'paedophile'. But British-word 'pedophile' means 'somebody who loves feet' (a foot-fetishist), from the same Greek root as 'pedal','pedestrian','centipede', etc.