All you'd need to do for that is download paint.net , find the files for the leather shirts, drifter pants and boots in game, copy them and change there name to something else, paint new colour on them in paint.net , then make duplicate and rename the items in FCS, and add in the new texture path that it needs to draw from. Then add them to a trader or a start and you can.

I would but I don't have Kenshi installed.

Such a great thumbnail, I wish those clothes were in game :(