POC color randomizer is what ur looking for, I wish it was a thing in game.
This mod allows to set freely the colors, banners and shields of each kingdom, clan or units: specifically or randomized. You can have the units to wear their very own colors and banners (each of you
www.nexusmods.com
Some of the mods in this video are out dated and won’t work but POC and kingdom color changer with the settings in the video work