I painted 132 Highlanders to split between Covenant and Montrose armies years back.
It was a bit of a learning curve but here's a few things I picked up on.
Muted colours for the rear ranks, brighter colours for the front.
Hose and trews are always on the bias (cross) jackets (mostly and plaid are always straight.
Painter thicker stripes to begin with and then an over stripe either over the original larger stripe, or inbetween. Hose, jacket and kilt were usually of differing patterns, so you can line up a number if figures and use the same pallete with different designs, change the colour of the over stripes or other things to make it look more individual.
This kind of explains what I mean...


Avoid giving the highlanders white hose or putting white in the tartan set.
Single colour (muted) hose and plaid is not unheard of, but neither are patchwork plaids and I wouldn't like to have ot paint one of them..!!