Barracuda molding paint.
I'm not aware of a black stripe on the rear molding (Tail panel?) of a 68 barracuda.
Those are painted red in the middle....medium cherry red to simulate the color of the tail light lens. Argent for the upper and lower sections.
Rough up the aluminum with a red scotch-brite pad and prep with some acetone or paint prep.
Use quality two part paint or something from these guys.
http://www.totallyautoinc.com/paint/paint.html. Its called tail panel red. They also have the Argent you will need.
I have had great luck on the parts I painted with their product.