Andrew,
Your color choice would very much depend on what "class" of clansman you're portraying for the `45 period. Look at period portraiture of clan chiefs, chieftains, and other upper-crust guys. They invariably are wearing bright red tartans of various setts, as bright as any "modern" red tartan. Why? The dye to achieve that bright red was imported and expensive, thus such a tartan is a status symbol.
If you are portraying a common clansman, then the earthier-toned shades as achieved from local dyestuffs are the appropriate choice.

Check out my website below, and the article on 1745 impressions....