I'm Canadian, so I was taught the English spelling in school (so "colour"). But by living in North America (and with the help of the internet and all), I think I'm more used to read "color" everywhere. The American spelling is also much more common in my field of study (computer sciences).
BUT! Even with all this, I prefer to use the English spelling of "colour" and all is friends (behaviour, odour, flavour, etc. )