Grenadiers converged battalions would indeed be of many facing colours (3, sometimes 2), since they were made-up of the Grenadiers compagnies of their parent regiments. As Jim mentionned, the practice was to group 'German' and 'Hungarian' grenadiers separately if possible.
So you would be wrong to have a Grenadier battalion with only one facing colour.
Grenadier battalions did have flags however (both Haythornthwaite and Hollins mention it). Usually a single Ordinarfahne (the 'yellow flag') As per Dave Hollins 'In 1805, the Grenadiers were formed up as the first battalion of each regt, but were still usually massed into a reserve. In 1806, they reverted to their old battalion arrangement. **Only in 1805 did they carry their regt Leibfahne otherwise it was a single spare Ordinarfahne.**'
Here is a list of the Grenadier battalions in 1809. Parent regiments of Grenadier Battalions are shown besides the number of men. I've also included the facing colours for each battalions.
3rd Division FML Lindenau
§ Grenadier Battalion Leiningden (742): 25/35/54 sea green, apple green, crab red
§ Grenadier Battalion Portner (713): 44/46 madder red, dark blue
§ Grenadier Battalion Georgy (745): 16/26/27- violet, parrot green, emperor yellow,
§ Grenadier Battalion Wieniasky (837): 11/11/47 pink, pink, steel green,
§ Grenadier Battalion Demontant (778):13/40/43 grass green, carmine, sulphur yellow
§ Grenadier Battalion Legrand (744): 9/55/56 apple green, pale blue, steel green
§ Grenadier Battalion Hohenlohe (708): 1/29/38 pompadour (dark red), pale blue, rose pink
§ Grenadier Battalion Hahn (523): 2/33/39 emperor yellow, dark blue, carmine
4rd Division FML d'Aspre
§ Grenadier Battalion Brzeczinski (610): 24/30/41- dark blue, light pike grey, sulphur yellow
§ Grenadier Battalion Puteany (682): 14/45/59 black, poppy red, orange-yellow
§ Grenadier Battalion Scovaud (665): 4/49/63 sky blue, light pike grey, light brown
§ Grenadier Battalion Scharlach (706): 31/32/51 emperor yellow, light blue, dark blue (Violet)
§ Grenadier Battalion Mayblόmel (727): 8/22/60 poppy red, emperor yellow, steel green
§ Grenadier Battalion Oklopsia(659): 12/20/23 dark brown, crab red, poppy red
§ Grenadier Battalion Bissigen (700): 3/50/58 sky blue, violet, black
§ Grenadier Battalion Kirchenbetter (713): 34/37/48 madder red, poppy red, steel green
You can look at my website for some help on the Austrian army (my favourite).
Iannick
Clash of Empires link