As expected Ford at Dearborn expected and wanted to have all Mustangs and Cougars built in 69 with window adjusting plates painted body color. They were often placed on the cowl panel and painted when the rest of the car was painted as indicated by the shadows they left there and as shown below. Of course there were sometimes mistakes and a few cars had the plates installed inside (non-body color side) outward. Human error from what the survey has shown not a change in production. Of course the plates in some rare cases could be dropped and lost require a quick replacement with non-body color plate filling in.
Typical look of the vast vast majority
Here is an example of poor workmanship. Drivers has a non-body color plate while the passenger side received a poor paint application. Since the one plate does not show body color around the edges this may have been a replacement after the other was dropped or simply the painter missed spraying this one. From 9F216xxx