Ah...the planning stages - often my favourite part. Of course, the execution holds much more rewards but often seems elusive. So it goes...
Anyway, undaunted, here are my initial thoughts on the Army of Sinistria, which nation being a little known principality in Western Germany.
The infantry consist of the Guard; the "Old Line" - that is, the regiments with long established histories; and the "New Line", regiments newly raised or of less "noble" lineage. And then there are regiments of "Light" infantry. All regiments have flank companies of grenadiers and lights. The whole organization is rather "French" - go figure: I'm using French figures to represent them! :-)
The "Old Line" will be in black with green small clothes and trousers, reversed for the drummers. Light troops all in green. Units of the "New Line" are in green jackets with white small clothes. The Guard are all black.
Edit: on consideration, I think that most of the "Old Line" will be black with green, but one unit will be green with black. The "New Line" will be some in all white and some in green with white - so basically "Army of Italy" - just to keep the more historically minded happy! ;-)
Haven't decided on turnbacks and cuffs yet.
Artillery are probably all black, or green with black.
Cavalry I haven't thought about. Probably all colours for the Hussars, green for the Dragoons and Black for the Cuirassiers.