The vast majority (if not all) the Baltimore built '67 GTOs I have seen at shows have body color painted extensions (just like Tempest & LeMans cars have). Now, I am NOT saying that ALL Baltimore built '67 GTOs were built this way, but I have seen way too many (very high percentage) of Baltimore cars with body color painted extensions to assume this is what was done at the Baltimore plant. Conversely, I have never seen a Pontiac built with body colored extensions. As for the other plants that built '67 GTOs (Framingham, Kansas City, or Fremont), I am not sure.
I believe the designers intended the GTO extensions to be painted black to match the grille bezels. The question is why the Baltimore plant did not follow this painting procedure? Perhaps this information "fell through the cracks" at the Baltimore plant. Or, maybe someone in management at the Baltimore plant decided to skip the black paint for GTO extensions as the Baltimore plant built relatively few GTOs (compared to the Pontiac plant), and therefore thought it wasn't worth the hassle. Unfortunately, the person to ask is probably very old or dead by now, so we probably will never know for sure.
BTW - The assembly manual makes no note how these extensions are to be painted.