I think you will find three plaids. Some Scots freak out when you call them plaids instead of tartans.
One tartan is a hideous yellow and black. Another is predominantly green and the other a brownish color. Some stories I have heard are that the yellow is the tartan of the McLeods (MacLeods) of Skye and the other two for the clans on harris and Lewis. Try a libarry for some history of the clans of Scotland.