I'm assuming you are trying to turn the harnesses white.
In the NL2MAT editor, go to the basic tab and tick the override diffuse, override ambient and override specular. Then change the colour for each of those options to grey (any shade of grey should do). It should fix the recolouring issues.
I've also uploaded a new revision with this change already done. So you could just download it again instead of messing with the options.