What they are referring to is that Prior to 73" ,,,the engine compartment, wheel wells and underneiths were brushed on black.. In 73' ,, only the bottom leading edge of the rockers were black,,, the engine compartment as everything else was body colour..

Your 70' to 73' model years front truck compartment were all painted body colour as well,,,, including Karmen bodied cars for 71'... If your car was metalic,,, there was little or no clear coat in the front truck compartment and it had a very dull appeareance..

Hope this helps...
Robert......