I knew the word "naked" would draw people's attention 
I have several N scale IM steel reefers and some have paint directly on plastic. The bodies were molded in orange plastic and the lettering was applied directly to the plastic. These are realy nice cars, but the painting directly on the plastic doesn't sell itself as well as paint on paint. Has anyone weathered these and is there any difference with them vs. painted cars? I really just want to tone down the plastic glare. Any suggestions?
Actually... I think I know exactly which ones you mean. I think it was the first run IM did in the 90s. I fondled some at a hobby shop and they looked unpainted to me too. Very translucent and plasticky looking. I actually wrote to IM asking why they would produce (then) brand new cars and leave them unpainted?! They replied to me by sending a small package with a sample orange reefer body. They said that it *WAS* painted. Sure enough, those reefers are made from translucent orange plastic and painted with translucent orange paint! Weird! I wouldn't have belived it if I didn't examine it up close (where I could see the hidden areas where the body wasn't painted). I still have that car body.
So, don't worry, weather them like any other painted car. Besides, weathering bare plastic shoudln't be any different than painted plastic. What makes a differerence is the glossiness of the surface. If the surface is not flat then things like pastels will not stick well to it.
