It's for the thick molding that goes around the car for stopping door dings and such. On the bumper of my '85, it's actually a molded into the bumper, rather than something that is stuck onto it. The other molding pieces either stick on or bolt on to the body. The trim black color looks great, and is accurate for an '83, but I like the trim black color (satin) when a car is painted black. My car isn't 100% accurate in how I had it refurbished (I hate the word "restored"). The changes are subtle, but certainly could be reversed if necessary.
To show you the trim, here is side shot of the car -
