Quote Originally Posted by Southern Breeze

The colors referred to in the thread count are specified as in heraldry (though it should be noted that tartan patterns are not heraldic). The exact shade which is used is a matter of artistic freedom and will vary from one mill to another as well as from one dye lot to another within the same mill.

Source- Wikipedia.
Yes, that does make sense. I didn't understand what a tartan specification was actually specifying. That means I had better not just specify a tartan by name because I will have no idea what I am getting. The tartan name is only the BEGINNING of the specification. That's very good to know.