Side note: English is a "Germanic" language but over 50% of English words have their origins in Latin, so there is a convincing case to be made that English is not in fact a Germanic language and is instead an amalgamated language of Germanic and Latin roots. Thus, there could be considered to exist two (almost exactly alike) dialects of English, one based on Germanic roots, and the other based on Latin roots. In this case "Color" would be the Germanic version, while "colour" would be the Latin version, but both would be correct, in different dialects.
English is a Germanic tongue, there's no doubt on that. It evolved from the truer Old English, but was gutted by the French-Normans and to this day has a nefaste amount of backstabber words. But it's Germanic, the wordstock is mostly Italic, though. And colo(u)r is a Latin root in both spellings - from French couleur. Hue, shade, and cast are the Anglish (what you talk about, truer Germanic English) words for colour, each from Germanic roots.
All of the English speaking world and former British colonies spell it like colour.
Well. obviously excluding America (and Liberia). Sometimes Canada spells things the American way as well.