Some of the more modern District (and other) Tartans do have symbolism in their colours. Here's one for example, the symbolism behind the tartan of the Northwest Territories in Canada:

Mrs. Anderson-Thomson chose the colours for the pattern. She wrote that green represents the forests, white the frozen Arctic Ocean, blue the Northwest Passage, gold the mineral wealth of the NWT and the red-orange, which she describes as "autumn colours" represents the barren lands or "Arctic prairies." The tartan also contains a thin black line representing the northern treeline.

-- http://www.nwtpipeband.ca/nwt_tartan.html
In the preface of "Tartan for Me!", Dr. Phillip Smith, a noted Tartan Scholar, deals with a number of myths about tartan. One myth states that there are "hidden ways" in a thread-count that spell out a clan's name -- a "hidden message", so to speak. Dr. Smith debunks that myth, and several others. I don't have my copy here at work, but I will transcribe that section tonight.

I'm sure Matt will also have a good deal to add to this thread! :mrgreen:

Cheers,

Todd