As far as I know....
Aside from engine size, all the Rallyes came with a black tail panel, I think orangosol black or something like that. The Rallye cars for '72 could have either a 318 as the base engine or 340 for the optional engine so either engine could have the black tail panel.
Non Rallye cars had the Argent silver tailpanel. I don't think any '72 cars came through with a body color tail panel.
To get more technical, if you look at some of the original sales pictures, the black tail panel had argent silver tail light buckets.
Here's a pic, not a sales pic, but you get the idea.