There may not be one. All the Ford prints say is "insulation (to be) 20% pure rubber, hard dyed and glazed cotton, oil resistant varnish." No color is specified and the Releases have no further information.
The vendors have different colors for different years. I wonder what info that's based on?
The brown plug wire the suppliers sell looks nice, but the black with red tracers and the orange with black tracers looks from a much later era.
I've found another option. These guys sell a 9mm black coloured plug wire with no tracers for $2 a foot. A solid black colour will also perhaps hide it's age better.
In the close up photo it looks a greenish-black so I wrote to supplier and he replied:
"The 9MM black spark plug wire I have does not have green in it. The resolution for the picture on our website was a bit high which gave it a hazy green tint. ... The appearance of the wire will differ a bit depending upon the batch. This spark plug wire is a stranded copper core wire with a PVC insulator covered by a lacquered cloth braided covering. This wire is what you might call a satin black as a lot of the cloth shows up unlike the glossy black wire that has almost not cloth showing."