In the mid-late 70s. it was common for dealers to use a cheap undercoat job to help close a deal. "I can get it undercoated for you and have it ready Friday!"

Thus, a lot of cars, including my '84 S/E were undercoated with relatively little regard for the niceties of driveshaft balance, overspray on exhaust, or even cleaning before application.

So, a basic black is very common, and if a judge was giving a hard time about a neatly blacked out chassis that popped the details, then I'd offer the Michigan gesture of traffic appreciation and leave.