Just so. It doesn't 'render it meaningless' at all. As has been explained to you, Dick, cockades of various colours were used at various times to denote various allegiances, political or military. At the distance of a couple of centuries it isn't always possible to be precisely certain what manner of resonance (if any) any particular colour had for whoever wrote or sang any particular version of the song; though guesses can be made. On the whole, educated guesses are likely to be more helpful but, although mildly interesting, it isn't terribly important.

Diane's football analogy was a good one, though on a point of information white was the 'official' Jacobite colour, not blue. If you want to sing the song, you obviously pick the form that best suits your personal preference, and invest it with whatever subjective significance you like. Different people will make different choices, now as in the past. That's all there is to it.