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. )
I love certain words with the non-American English spelling, like humour, favourite and theatre, but for the most part I think the "u" is useless and I think words should end with "-ize" not "-ise." Though, I think it's all a part of phonetics as well: Alphabetized sounds (and looks) better with American accents while Alphabetised sounds (and looks) better with European/Canadian accents~