You can't go wrong with black but Acapulco Blue is one of my favorite Mustang colors. There are some I haven't heard of in the attached link. Beatnick Blue looks good. I'd keep it the original or a factory color.
I found the factory build sheets under the carpet of my '70 Mach One. It was interesting to see the color codes for the various parts that went on the car. ie: under front spring it said gld pnk, the springs have a gold and pink paint stripe/ dab on them.
