Apologies for the necro/late response, but if there is anyone who wants their own colour and it is not available here, simply:

1. Subscribe to any of these Faction Colour mods,
2. Keep note of the mod number (it's the "?id=<number_here>" in the mod page you just subscribed to
3. Now open the Forgotten Construction Set (FCS; located in same folder as Kenshi.exe)
2. Close the first pop-up box by hitting ESC (you don't need to select anything here)
3. Look for "Open any" at the top of FCS. Click that, then search for the mod location (for me, it's C:\SteamLibrary\steamapps\workshop\content\233860\<Faction Colour mod number here>
4. When you've found the folder, open the .mod file using FCS.
5. Inside, you will find the faction name (Nameless) and the Player Faction Colour file.
6. Open the Player Faction Colour file and you will notice that there are two colours.
7. Here, you are free to change the colours to whatever suits you, have fun.