Well, having looked at the references, it's still not entirely clear.
Of the German regiments that embarked for North America in British service, the following had blue coats, with red lapels and cuffs, as the K&C figures do:
from Hessen-Kassel, regiments "Prinz Carl", "Erbprinz", "Von Mirbach", "Lossberg";
from Hessen-Hanau, regiment "Erbprinz";
from Brunswick, "Von Specht"
The Brunswick troops can be ruled out, not because they aren't Hessians, in the literal sense, but because of the grenadiers' cap plates, and because the color carried by the one officer figure is definitely from a Kasseler regiment, Regiment "Trümbach". But the K&C Hessians can't be from Regiment Trümbach, because that regiment did not wear lapels.
Of the remaining regiments who wore red lapels, only Lossberg wore plain lapels, without lace (though Trenkle shows them at the time of the Seven Years War, with a plain lace border). The other regiments all had either lace borders, or lace-trimmed buttonholes, or both.
Lossberg was a fusilier regiment, and it was part of von Rall's command at Trenton. If this is the correct regiment, then K&C's grenadiers represent the grenadier companies of the regiment.
However, Lossberg's colors had a scarlet field, not blue, with green darts in corners. Their lapels were also more of a scarlet color (in Mollo's book, it almost looks orange, a trick of the printing process), rather than the darker, poppy red (auf gut deitsch, ponceaurot) of the other regiments.
I've said it before-these are minor details that most probably wouldn't mind, and that wouldn't keep them from buying the figures. But I can't get past the moustaches the officers are wearing-gentlemen didn't wear facial hair at this time, with the exception of some hussar officers. Also, the officer carrying the flag is wearing riding boots, so he must have gotten knocked off his horse. Only officers whose duties permitted them to ride would have worn boots; otherwise, they wore gaiters.
But they fill a void in the collecting world right now. The only other option for anyone who wants Britain's German allies is Imrire-Risley or Preiser kits.
Hope that helps, and if anyone else has more research, please join in!
Prost!
Brad