Heroes 5 Armageddon’s Blade

Regarding player recognition, in the file responsible for the hero's appearance on the map (the character file, which contains links to the model and animation set), there is a line with links to colored models.

I don't remember if there's anything similar for buildings, but you can experiment.

Added 2 minutes ago
By the way, how long did the castle retopology take? Can you post a screenshot of the geometry (I mean the mesh) just out of curiosity? Especially the "complex" areas where it's difficult to save polygons, like stairs, arches, and so on. I'm interested in how you solve these problems.

Added 16 minutes ago

Textured Citadel Buildings:
https://www.youtube.com/watch?v=zl5UIQbegqU

It looks very, very cool. It's perfect for the city screen. How did you make the ground, and what did you use? By the way, there might be some problems with the city screen. The position of objects in it can be anything. The position of the camera in the window for selecting a specific object can also be adjusted, but it's very tedious. However, there seem to be problems with the camera in the castle menu (the camera that does the cinematic fly-around). I'm not sure if it will be possible to create a new one.
But, you can always use an existing one. Something without any particularly specific movements, from the Mages, Orcs, or Elves. However, if you do, I recommend loading the main buildings from the city as a reference, the fly-around camera of which you will be using, and adjust your buildings to roughly match their position. This way, you can be sure that the camera won't fly through the building.

Plus, you'll save a lot of time and effort if you use an existing camera for the building in the building selection menu. You don't necessarily have to put the blacksmith where it was in the donor city, but if there was something in the place where you want to put the blacksmith, you can use the camera from that something instead of spending several hours calculating the camera coordinates for your unique building with its unique position.

Honestly, as a donor city, I think the Orc city looks best. The camera does a large panoramic fly-around and rarely gets close to the buildings, so it won't pass through anything. There's plenty of space and room to place buildings.

In general, I've dug around in the city screen files quite a bit, and I can tell you that trying to do anything there is quite masochistic. So, I advise you to approach it intelligently and just copy existing coordinates. This way, at least something can be done without going crazy.