the models won't export.

I apologize for posting in this thread: I just wanted to quickly send a message while I still have an internet connection, rather than searching for the right thread. Besides, this issue is also discussed here.

I would like to understand what is meant by "recoloring" units. I've noticed that some mods have excellently recolored creatures, and I'm trying to do the same, but I can't seem to get it right. I change the model and textures of a Death Knight to that of a Paladin, and as a result, there's some kind of mess on the horse with a smeared helmet and no eyes. I don't need a Paladin to be there; I just want the Death Knight to have armor of the same color. Also, I can only replace the textures of a specific part of the monster, for example, the entire body at once, but I can't recolor the sword separately.
What am I doing wrong? Do I need to create my own textures and then link to them? Or should I use existing ones? For example, if I recolor a dragon, the shine in its eyes always disappears. I hope for an answer.