I'm not at all sure that this wording in the code was deliberate. I agree, technically re-identifying a wire to make it white is not allowed.
Personally, I disagree with this rule. Argument aside, not a single supply house here carries #6 or #8 wire in any color but black. Ironically, sometimes the box dtores do!
Frankly, I am simply delighted when ANY attempt is made to properly identify conductors.
