After finally locating a blue FUEL lens, I was just going back over my other lenses to switch back to the original & away from the Scott Drake imitations and noticed my park brake warning lens previously had taken on a bit of heat from the bulb.
These early ones are different than the later and 68's as they are back-lit and look basically BLACK until the bulb lights, then all you see is the FONT of the particular panel function (red, font for the PARK brake light)