The graphic of the 42nd Officer is interesting. He appears to be a pre-1759 company officer (no lapels or bastion-loop lace). The apparent blue waistcoat is interesting, as is the bonnet (which has a diced band and is apparently cocked/stiffened - this is a detail that we associate with the 42nd's post-1768 uniform). Unfortunately, there are no views of the officer's tartan. Of course, the amalgamation of 1/42nd and 2/42nd after the latter came to North America, and the Board of General Officers-approved uniform changes for the regiment meant that this uniform was a short-lived one for 2/42nd officers. I presume Col McCullogh covers it in his book, but Capt Stewart's order book describes in some detail the preparation of new uniforms for the 42nd during the spring/summer of 1759, when the entire regiment went into blue facings, bastion-loop lace and lapeled uniform coats. Up to that point, members of the old 1/42nd had coats with pointed lace loops, no lapels and buff collars and cuffs, even though the regiment had been made "Royal" in the summer of 1758. That word didn't reach the 1/42nd until after their new annual uniform issue in the old pattern had reached it and been provided to the troops.

Luke, you are right about regimental officers apparently flaunting the King's dress regulations in some respects. From my reading on the subject, I have come to the conclusion that British officers (including those in Highland regiments) cared more about what their Colonel wanted them to wear for dress as opposed to what the King and his Board of General Officers had approved. If they were in workaday undress, the officers apparently had even more discretion as to the details of their uniforms.