Maybe he's using plastic nuts like these:
http://www.cliffusa.com/info.asp?ID=304
http://www.cliffusa.com/info.asp?ID=304
> It's not just the washers. The nut and washer are both colored. Let's
> ask him about it on Muffs. I bet he paints them. And if he does, how
> does he tighten the nut without damaging the paint?
>