There are also ospreys about the subject including those for Scottish wars against the english both Man-at-arms and campaign series.
Of which, the early one on "Edward I's Scottish and Welsh Wars" is, to be honest a bit ropey, and best avoided. Very much a product of its time, it contains a lot of info that has since been dismissed as Victorian propaganda/romanticism. For example, the blind insistence that Scots archers used a "short" bow, rather than the "long" bow of the English/ Welsh. The later one on Scots Rennaissance Armies is a good bit better, with some interesting info.
Lowland Scots soldiers were dressed/ outfitted much the same as any other North Western soldier of similar rank/professionalism. "Uniform" was initially restricted to a simple white St Andrews cross sewn onto the outer layers of clothing or soft armour (painted on to metal plate in the later eras). later, following the development of the retinue system, professional soldiers in the service of te major lords would wear colours or badges identifying their masters, in much the same way as English, French, etc troops.
As for Highlanders, very little written info from the period is available. What they didn't wear was tartan and blue face paint...
Much would depend on what parts of the Highlands they hailed from; some areas had a strong irish influence, others a Scandinavian flavour, whilst others took on aspects gleaned from the lowlanders. Early tartan, or Breacan, may have started to appear towrds the later part of your period, but bore littel resemblance to tartan as it is marketed today; no bright colours, intricate setts, etc; think muted browns, the odd green or blue. It functioned almost as a sort of early camouflage when lying on the hills, as the dyes all camefrom whatever plants grew in the local areas, "clan" tartans didn't come into it!
Cheers
Iain