Honest Cpt. is is not difficult.
1) Paint the kilt a base colour, e.g. Mid Green.
2) Paint stripes with a contrasting colour, e.g. Red.
(I don't paint nearly enough stripes, but it looks OK in a unit/clan)
I normally do about three horizontal stripes (one in the middle,
one near the bottom & one near the top of the kilt.
Then some vertical stripes. I usually start on one hip & work around
spacing them out. Any errors in spacing are normally lost under an arm/shield/sword etc.
If you do a fairly light shade for your base colour (stage '1') the stripes can be done
with gel pens.
3) Draw some fine lines through the 'boxes' formed by the horizontal & vertical stripes.
Do this with a white gel pen, black (indelible) pen, or even a sharp 2B pencil.
4) On a (very) few figures in the unit, put 'dots' of a dark colour where the horizontal
& vertical lines cross. Again with gel pens if you are not confident about your
fine detail brush work.
5) Leave it all do dry (I leave it for at least a day, often more if I am waiting for a nice
dry British day

) and spray varnish it. This will protect the gel pen ink &, if you
have used a 2B pencil, turn the pencil line into Black.
6) Optional, spray it Matt Varnish (when the gloss is well dry) for a more fabrick look.
It really does take less time to do a group of say half a dozen, than for me to type this.

Give it a try. Highlanders are great in skirmish games too, & for that 3,4,5 or 6 will do.