HighKick
Master Black Belt
Let me take swing at this."Color" and "colour" are both correct spellings of the word. "Colur" is not. If I teach "color" and another instructor teaches "colour", I can explain to the students that there's different ways to spelling it. If another instructor spells it "colur" I will have a talk with them.
If I want to spell it "color" and my student is doing "colour", I can tell them that is a way of spelling it, but the drill today is "color". If I see them spelling it "colur", I'll tell them that it's incorrect (but also do my due diligence to see if there is a word spelt that way).
If 'color' and 'colour' are the same, (just from a different system for example), then it could be explained as regional differences for the reason. If another instructor spells if 'colur', this rings very loudly of what you are planning to do.
Paint a white horse grey and it is still a white horse.