Hello @bigsmit19 i recommend you to take a look here:
https://www.reddit.com/r/0ad/comments/w1ge65/comment/ijrkwue/?utm_source=share&utm_medium=web2x&context=3
Athenian cavalry javelineer portrait has a linothorax texture different than the ones used but it still represents the unit well.
Gaul champion swordsman portrait has a different linothorax (simpler) than used by the unit (more colorful). Not sure about impact on recognizability (i checked, this word exists in the dictionary).
Also, Gaul javelinists and slingers are sporting tattoos in portraits which they are missing in-game (i guess they fashion temporary tattoos for the photoshoot).
Macedonian Argyraspides portrait has laurel leaves on the helmet which are missing in-game.
Persion champion spearman portrait is different than the armor used in-game.
Seleucid infantry javelineer has a different shield in portrait than in-game.
I think it helps to stick to a color scheme, for example, if it had metal armor, a unit has either bronze colored or iron/silver colored armor. If it has linothorax, then it has either white or brown colored linothorax etc. Then it is possible to have a high variation but also be easy to recognize