As a Canadian, I use "colour". Spellcheck can get bent.
I'll also note that spelling only started being standardized a couple of centuries ago, and sometimes the most ridiculous versions are chosen. I got to talk with the editor of the Canadian Oxford English Dictionary once, and she thought when they were picking which spelling of "porpoise" to use, they must have pinned all the options to a dartboard and let fly.
Najos said:
The reason it is spelled "color" instead of "colour" in the States is because in the early 1900's there was this movement to make English easier to understand and write. I forget all the details, but we basically took all of the U's out of any OU words and some other things before giving up altogether. I think Roosevelt was behind it, which is kind of ironic.
Edit: Found an article on it.
http://history1900s.about.com/od/1900s/qt/trspelling.htm
You're incorrect: American spellings were pioneered by Noah Webster, lexicographer of the first American English dictionary--yes, that Webster's Dictionary. Webster was a supporter and beneficiary of the American Revolution and wanted to "Americanize" the spelling of words [http://en.wikipedia.org/wiki/Noah_Webster#Blue_Backed_Speller] to differentiate them from the spellings of decadent and corrupt English aristocrats. Since Webster was hugely influential on early American dictionaries and early American schools, he got his way.