La compagnie des grenadiers du régiment  Royal Écossois
The Regiment “Royal Écossois” (1744–1762) was raised by Lord John Drummond (1714–1747) for the King of France, Louis XV (1710–1774), who supported the Jacobite rising in 1745. The officers of the regiment were always Scottish, mostly Highland, as were the majority of “other ranks” in the early years of the regiment. Later, during the Seven Years War (1756–1763), soldiers from Germany, and many other nations, enlisted in the rank and file of the regiment.
The Royal Écossois fought in 1746 at the Battle of Culloden for the Jacobite prince and pretender, Charles Edward Stuart (1720–1788), also known as Bonnie Prince Charlie, who claimed the British throne for the House of Stuart. The Battle of Culloden ended in a disaster with countless casualties in the ranks of the Jacobites. Those soldiers of the Royal Écossois, who had survived the massacre, were either taken prisoner on the battlefield or surrendered to the Government forces in Inverness. Since they were regular soldiers of the French army, they were pardoned and returned to France.

In the early years of the Seven Years War, between 1756 and 1760,  the Royal Écossois, as part of the “Brigade Irlandaise”, were moved between various garrisons on the Channel-coast to pose a threat of invasion to Britain. After the “Annus Mirabilis” of 1759, when the British had conquered French America, most of the Irish Brigade, including its two Scottish regiments, were sent to join Marshal De Broglie´s French army in Germany, where they defended Marburg in 1761. At the  battle of Vellinghausen (1761), as part of the losing French army, the Royal Écossois were taken prisoner by the allies. In 1762 the regiment was disbanded.
The members of Jacobite History est. 2010 proudly portray “La compagnie des grenadiers du régiment Royal Écossois”, one of only two units of the French army wearing Scottish Highland Dress.
(1) 2e Carte Militaire ou Liste Générale des Troupes de France, anno 1754
   "Les Grenadiers sans Culottes"
(2) Ettrenes Militaries, anno 1758
   "La Compagnie des Grenadiers est habillée à la Montagnarde Ecossoise"



P.S. As one can see, the sources mentioned above are from post-Culloden times. However, to be honest, NOT wearing Highland Dress during the Fortyfive.. but then wearing Highand Dress just a couple of years later would not make sense.
In case someone might not be happy with our research, please feel free to prove the opposite by presenting historical facts like we did — authentic descriptions of the grenadier´s clothing from the era.