Since most tartans were created relatively recently, the argument realy doesn't hold any validity. Now, for the patterns is us ages ago, I would be willing to bet that certain regions used certain colors based on what was available. Of course, the wealthier folks could afford to import the more expensive dies and thus have access to more colors. Some could very well have tried to show off their wealth by having more colors, but as Matt's research has shown, it was not a formal (or informal) system of identification of station.