Jeff,
could it be that the door panel was painted to match/blend with the carpeting? ....................
70 is an odd year in this detail and as much may have to do to when the car was built. But of course the original question was the trap door matching the exterior color of the car
Looking at original cars I can only offer (unfortunately for this survey there are allot of black interior cars built)
0F02F107749 - White interior with Charcoal trap door and panel below window. Similar pattern for white (though it lacks the two corners pieces being black) to 69 handling of the white interior.
0F05Q1105xx - Ginger interior and the trap door is ginger to other interior panels not the darker carpet
0F05R144530 - Ginger interior and the trap door is ginger to other interior panels not the darker carpet
0F05H111886 - Green interior and the trap door is green to other interior panels
0F05M119187 - Blue interior and the trap door is blue to other interior panels
0F05M122118 - Blue interior and the trap door is blue to other interior panels
0T02G114472 - Ginger interior and the trap door is ginger to other interior panels not the darker carpet
Just what I have