From my own research, the colors of the tartans were almost incidental depending on where the cloth originated. The local plants used for the dying process were more the reason a color was used then any meaning. Altho i do remember reading that one Clan changed one of their setts to include more red to commemorate the loss of life in battles. But sorry to say, i can't remember which tartan it was. (I will look thru my research to locate said piece of information)