Installed the colour palette mod and decided It wasnt for me and uninstalled, however once I did I found I could not have games with any more than two other AI players. The slots were filled with error messages if any slots were added and no dropdown menu would appear when clicked.
I decided to first verify files after unsubbing from the mod. I validated 1 missing file but issue still persisted. Decided to then reinstall game but it didnt fix the issue.

Currently reinstalling after deleting all ES2 files from steam folder and documents to see if the issue resolves itself.

Yeah, I looked at my mod and there's nothing wrong in the coding to cause it from my end, at least according to my knowledge modding Endless Legend for the last few years. There's a few bugs it seems associated with the game state in the menu and not fully implementing or changing things. If you simply switch palettes without mods, the new palette ie color blind or Endless Space 1 will not take into effect until a full exit and reopen.