Today I'm just starting to get back into modding.
I am currently starting to review the "scout" units so that they are AOR for all Latin factions. For this, I will try to create a slightly different model between the "scouts" of the West, those of Eastern Europe and those of Southern Europe.
As AOR units, visual differences depend on recruiting faction, not recruiting area, both in terms of how they look on the battlefield and how they look on the unit card.
This gives the advantage of being able to choose a dominant color per faction, but if a faction moves very far from its territory, it will recruit scouts who will not have the local appearance (example: the Poles reach the west. They will recruit scouts in the visual style of Eastern Europe). That said, this scenario will likely be very rare and shouldn't be too troublesome.