Waterloo Remembered

I'm reading Paul L. Dawson's Marshal Ney at Waterloo and in it he quotes a passage from Cavalie´ Mercer's Journal of the Waterloo Campaign in which Mercer describes being woken before dawn on the morning of June 17th 1815 by the sound of musketry. He was then surprised to see "numerous white discs, which were continually in motion, changing place and disappearing." He says this "puzzled me exceedingly, and I could not even form a conjecture as to what they might be." Once the dawn arrives he realizes that what he has been looking at is "a corps of Nassau troops, lying on the ground, having white tops to their shakos."

I know that some Nassau troops had white shako covers, but the effect Mercer is describing sounds rather different to that. Does anyone know whether the tops of the shakos of Nassau troops were indeed white?