I think people should just agree to use the two words differently, like, use 'Color' as a noun and 'Colour' as a verb.
"The boy coloured in the outline of the painting."
"The color that he chose to use was green."
Though it is quite silly that in american english, Colour isn't a word, yet in the english language, it's vice versa; 'Colour' is the correct spelling, while 'Color' is incorrect.