OK I see that the tourie colour was used as one of the distinctions between the various sorts of companies that used to exist in Highland regiments.

I'm guessing that the Highland regiments were following the variously coloured pompoms used on the headgear of English regiments to distinguish the ordinary companies from the "flank companies".

Where this distinction usually shows up is in the wings/shells worn on the shoulders of the "flank companies".

As I recall these distinctions were done away with in the early 19th century.

For all intents and purposes all Scottish regimental touries have been red for around 200 years save for the London Scottish (and Dominion regiments which follow their uniform such as the Toronto Scottish) which wear a bright mid-blue and the Cameronians, who, being Rifles, wore dark green uniforms with full black trim and buttons. I think the Cameronian touries were black.