Here’s a survivor grille to assist with the black paint line.
This is an original 68 grille and note the plastic color is a tan or cream looking color. If you look back close to the first picture you can see that tan/cream color at some of the horizontal bars as the paint did not fully cover all areas. I would call the painted grille color more of a mix between silver and gray. Note the rivet heads for the bracket that was riveted to each end of the grille. I might or should have the formula of what we color matched if needed.
This was our NOS grille and note this 1983 (date on box) service replacement was a dark gray.
After painting it with a color matched paint to match originals!
After riveting brackets to grille!
Grille as we were installing!