Before modifying kit color we need to enable or confirm ?useteamrestrictions=1 is in your maplist.ini if youve already created your maplist.ini using the in game admin or modified it manually as with this guide: Maplist.ini
The files to edit are the Blue.res and Red.res files found at GroundBranch\Content\GroundBranch\DefaultLoadouts\Blue.res and GroundBranch\Content\GroundBranch\DefaultLoadouts\Red.res
Those two files can be found in the "Configuration Files" section of the game panel for easy editing.
Stop your server to modify them.
