How do Canadians spell colour (color)?

English speaking Canadians usually use colour.

French speaking Canadians use couleur.

Canada has two official languages, French and English. Their English is called Canadian English, and is a combination of both British and American English.

To answer your question on the whole they would spell it the British way - 'colour', although the American way - 'color', is not entirely uncommon.

https://en.wikipedia.org/wiki/Canadian_English

Not ALL Canadians spell the word "colour", to be fair Francophone Canadians spell it "COULEUR".

C'est la vie!

http://french.about.com/library/begin/bl_colors.htm

Ah, but those French-Canadians still have a 'u' in their colour!

True, billy but they also have an "e" which makes their spelling different than both the American and English Canadian spellings.