Agree that they were suppose to be and are the vast majority of time body color. And I would suggest they be returned that way. Seen a few even installed upside down (painted side towards the door) by mistake.
Here are a couple of original examples to illustrate how 69 Dearborn's were (guess that is the one your working on) The painting was a results of the workers normally placing the plates on the cowl during the cars exterior paint application. Example below is from a coupe or convertible - the reason why there are two pair of plate shadows. It its a later 69 car this area is covered with engine compartment black covering over this detail