I don't remember the HLI wearing Mackenzie tartan. The Seaforth Highlanders wore that tartan, as the Earls of Seaforth were MacKenzies.
So many of these different regiments, were raised to prevent the 'Laird' from having his land and titles taken away if he didn't provide men to serve in the British army. They are now gone, and have been amalgamated into the amorphous 'Highlanders'
Giok