According to Watson, page 103:
“Patten, when he accompanied Somerset’s expedition against the Scots, took particular notice of similarity in dress of Scottish lairds to that of their followers. Lairds and barons, he remarked, wore not only the same jacks, covered with white leather, as their men, but the same white leather or fustian doublets, and usually white hose.”
The Duke of Somerset invaded the Borders in 1547.
Fustian = thick, hard-wearing twilled cloth with a short nap, usually dyed in dark colours