If you do a search you'll see that the discussion has come up before. You'll find my documentation of a 69 Dearborn restoration at that thread - with a fair number of pictures
http://www.concoursmustang.com/forum/index.php?topic=10.0Everyone USED TO use red oxide but in the more recent years the batch colors is more an accepted finish though red oxide has been documented as used during specific periods of the production year. It appears that for the batch paint they started with an epoxy primer then added allot of left over paint from a time period (may be a day, a shift....) before the car was shot.
Since its just basic colors if you add enough of every color in the rainbow you will get a almost black color. At the same time we know that every color was not available not applied in equal numbers so if there were more blue or green paint left over than the finished product that batch was tinted towards that color. More whites or light yellows the color was lighter. More metallics....... well you get the idea.
As always its best to match exactly what you find on your particular car and document it (I keep a large bag (moving into multiple bags) of samples cut from the floor boards of restored or repaired Mustangs and Shelbys.
If you car lacks any evidence of the original color the second best choice is to seek out a car built the same day or week and at the same factory.
Bottom line - restore it as you find it (unless there is a suggestion that the car has been played with) and as you have been, document, document