"Brown grain" seems to be a telltale sign of multi-generation duping, particularly in the late 70s/early 80s. I was just watching The Great Muppet Caper on HDNet Movies, and the opening credits (with the hot air balloon) showed a blue sky full of "brown" grain.
That Stormtrooper shot was duped to add in the Falcon, and it was diffused, and it was filmed in standard Panavision rather than VistaVision, so it makes sense that it would look grainier.