The last years of the "Scots brigade" in Swedish service is poorly covered by historians compared the early years in Danish & Swedish service. For example Fallon's excellent PhD skips the period completely and just describes the final years of 1637-1640 in a short chapter after having covered the 1620's and early 1630's in great detail.
This makes it hard to track the various Scots regiments, particularly as when command was transfered from one officer to another or when several depleted regiments were reformed into a new one.
By 1636 military situation for the Swedes was increasingly desperate and the war finances had almost collapsed due to the loss of major sources of income. (The collapse of the Heilbronn Leauge which had funded most of the army in 1633-1634, losing the contributions levied on the occupied parts of southern Germany and having to return the rich Prussian ports to Poland-Lithuania)
This had a serious impact on the apperance of the soldiers themselves, it proved impossible to issue proper military clothing to such recuits who had gotten it in the days of Gustavus. The native Swedish concripts & the Scots were particularly affected by this.
Cunningham's Scots regiment formed part of the Scots brigade at Wittstock. It was raised in 1635 for the army tasked with defending the Prussian ports against Polish attack. In the end the situation was resolved by the treaty of Stuhmsdorf and the troops in Prussia were sent to Germany as much needed reinforcements.
While in Prussia the Scots were described by French eyewitness Charles Ogier. They were "poorest of all" and sleep in the open beneath the dubious shelter of trees in disorderly groups rather than making a proper camp. They were worse off than the Swedish conscripts who went barefoot and were clad in rags.
By contrast the German soliders were skilled veterans for the most part and made an orderly camp complete with roofed huts which looked like a small village. As they had their wives and children with then their clothing was in good order as it was properly washed and mended.
Ogier also describes a flag carried by the Scots troops, it was red with a white cross on a blue field in one corner. I.e the cross of St. Andrew.
Ogier provides no detailed description of the clothing worn by the Scots so it is impossible to say if they wore tattered lowland or highland dress. However he notes that many of them were Catholics which could imply Highlanders if I understand the religious divide in Scotland correctly.
Also Highlanders were considered to be very poorly dressed by contemporary standards and "Irish" i.e Gaelic speaking troops were often refered to as being "naked" by contemporary Swedish observers before they were issued with proper soldiers clothing.
James Karr's regiment had served with Baner since 1634 and in that year it was described by Axel Oxenstierna as the best of all the enlisted foreign regiments serving with the Swedish army. It may have contained a considerable part of veteransfrom older Scots regiments that were reformed or disbanded in 1633-1634. Karr was highly regarded as he was promoted to Major-General and would probably have risen to even higher rank if he had not been killed during the siege of Leipzig in 1637.
The final regiment of the brigade, Lindsay's, is a bit of a mystery as it suddenly appears in the Wittstock order of battle yet there is no trace of it in previous musters.
Lindsay had probably taken command of the regiment just prior to the battle but at the moment I can't identify the previous commander.
Cunningham, Karr and Lindsay are the only regiments which I can indetify with certainty as Scots. The Swedish habit of employing Scots as commanders of both native Swedish and German units makes it impossible to indentify the nationality of a unit based on the name of the commander alone. Also at Wittstock you had regiments commanded by Forbus, Gunn, Leslie and Ruthven but at the moment it is impossible for me to tell if last 3 units were Scots or Germans.
"Forbus" was Arvid Forbes whose father was a German-Scots cavalryman who married the daughter of a Swedish admiral. Born in Finland he was nick-named "Finn-Forbes" by other Scots and led German troops in Swedish service.