Have not found allot blacked out but would guess it was for looks. Ford tried a number of things to improve the looks - some so minor you would not think they would care - but someone did at least at the time
It looks to me, from the bubbles in some of the paint and the runs that it was likely a black lacquer that was possibly left in a coffee can or such so it would be handy to apply. The guy grabs the container, stirs it a bit with the used brush, introducing bubbles into the paint, Since it sat out open the paint would thicken up, helping with the bubbles being trapped and producing the look I seen on some
Just some thoughts