Peter,

Regarding that Red/Yellow Sett in the early Black Watch images, there are like 3 sets of images, multiple artists that show that. I almost wonder if perhaps they really did have a tartan like that?

There is of course, the Mutineer Images, this one of Farquar Shaw



But then there are these images from the Continent, that also show Red/Yellow


Another watercolor, from the ASK Brown Collection, hard to tell if its red yellow or something akin to Blackwatch:

The hose are certainly red/yellow





Then there is this oil, "Fashionable people thronging St James's Park", c.1745 Attributed to Joseph Nickolls





With woodcuts and watercolors there is always artistic licence or disconnect between the engraver and the person who colorized it, but sure does seem like a lot of "Artistic Licence" in the same vein in all these 45/46 era images. I have no idea if either of the 2 Col's prior to Murray have papers that survive that might shed some light on this.