Perhaps I should have bothered to read Scarlett's article in its entirety again, rather than just the part I thought was pertinent to my post. In the last paragraph of the Background section, he says what he calls the "MacDonald type" is "predominantly red", and "has a broad green stripe with a narrower black or blue one [sic] each side...." That sounds something like the MacDonald of Sleat tartan, rather than the conventional clan tartan (which is not attested before 1810). There's another article by Scarlett here. It's briefer, but it has more to say about the origin of clan tartans. The other part I missed was Scarletts opinion that the "dark setts" (blue-black-green) originated either with the military or with George Buchanan. That's not much different from what I had supposed.
Quote Originally Posted by sirdaniel1975 View Post
They were completely capable of developing dark colored tartans with vegetable dyes.
Yes, they were. However, as a general rule, the green—at least—of the tartans produced before the mid-19th century was quite lighter than the green of the tartans produced in modern colors. Other colors also tended to be somewhat lighter, although not nearly so light as the modern "ancient" tartans. I'm not sure why it changed. It may have to do with Victorian tastes in color, or it may be that early chemical dyes had a limited (dark) palette. Obviously, chemical dyes can produce all sorts of shades these days, since they're used for the "ancient" and "weathered" tartans as well as the "modern" tartans.