For the Irish component of Montrose's men:
Alas we don't really know that much about exactly what form C17th traditional headwear took, so I went the monmouth caps route to represent Irish baraid. Most figure sculptors utilise images from Ospreys as their primary source material. I've also utilised a few rough brimmed hats, cabascets and morions to represent those who fought in earlier European conflicts. I utilised a quote for my clothing colours palette; Sir J T Gilbert's (History of the Irish Confederation and the War In Ireland 1641-1643) description of the Confederates fighting at Kilrush being almost indistinguishable from the bog due to the dark colours they wore.
Occam's razor is going to have any Irish flavour to their clothing being replaced by Hodden grey as their campaign drags on, their clothing wears out, and they replace it with whatever is available locally.
There is a new volume due soon from Helion, coauthored by Ed Furgol, on Montrose's Army. He gave a taster on it at last year's Century of the Soldier conference. For balance a second edition of his Covenanting Armies is in the pipeline too.