Thanks for re-publishing Richard Tennant's excellent review of Leval’s "German Division": “The German and Dutch Troops in Spain”
I have just read the most recent instalment, “Chapter 2 Part II: Troops of Hessen-Darmstadt”
First a slight digression and confession: I started collecting and painting this infantry division together with my brother Melvin, in Connoisseur and Elite Miniatures 25mm-28mm, over 35 years ago - hence my interest.
There are a couple of sources post-1989, when this article apparently was first published, that provide some further insights into these troops that might be of interest to some.
Jack Gill in “With Eagles to Glory" reports that the Gross-und-Erbprinz Brigade (before departing for Spain) comprised:
• Gross-und-Erbprinz Regiment
• 2nd Leib Fusiliers Battalion.1
The former wore dark-blue jackets with yellow distinctions and the latter dark-green and yellow, respectively.
Gill explains the unique composition of these brigades was of two musketeer battalions and a “semi independent fusilier battalion to perform light infantry functions.”
All battalions were of four companies, numbered: 1st (1-4) 2nd (5-8) although the first company in both musketeer and fusilier companies were “honoured with the title ‘Leib-Kompanie’” 2
Digby Smith in vol 1 of his history of German troops in Spain also reports, prior to setting off for Spain, the “brigade had three battalions on the Prussian model; two of musketeers and one fusiliers (light infantry). The musketeers wore dark blue coats, the fusiliers dark green.” 3
Both authors report the re-organisation of troops on French lines en-route.4

Notes
1. Gill, John H., With Eagles to Glory: Napoleon and his German Allies in the 1809 Campaign, (Greenhill, 1992), pp. 218-9 and 243-4
2. Gill ibid citing von Bigge W, Geschichte des Infanterie-Regiments Kaiser Wilhelm (2. Großherzoglich Hessisches) Nr. 116, Mittler und Sohn, Berlin, 1903, p. 102
3. Smith, D, Napoleon’s German Division in Spain, Vol 1, Ken Trotman, 2012, p. 31 referencing Keim, A, Geschichte des 4. Grossherzoglich-Hessischen Infanterie-Regiments (Prinz Karl) Nr.118 und seiner Stämme 1699-1878, Mittler und Sohn, 1879
4. Gill reports, “En route to Spain, this unit was completely reorganized along French lines into a regiment of two battalions, each of six companies. This was accomplished by distributing the fusiliers amongst the two musketeer battalions but had the negative result of hopelessly intermingling green and blue uniforms when the Hessians were formed for inspection.”
Best wishes
A