Color vs. colour
Color and colour are different spellings of the same word. Color is the preferred spelling in American English, and colour is preferred in all other main varieties of English. The distinction extends to all derivatives of the word. Colored, coloring, colorer, colorful, and discolor are the U.S. spellings, and coloured, colouring, colourer, colourful, and discolour are preferred outside the U.S.
Both spellings are many centuries old. Color, now regarded as the American spelling, in fact predates the United States by several centuries. In early use the spellings vied for ascendancy with several other spellings. Colur, culoure, and coolor, for instance, were all in the mix before the modern British spelling gained permanent prevalence in the 17th century.1 The American preference for color took hold in the middle 19th century thanks in large part to the conscious simplification of English spellings by people such as the lexicographer Noah Webster.