The info I have indicates the JF1 code was a high - impact color for 1972 and 1973. It was Mist Green for Chry., Ply. and Imp. and Pale Green for Dodge. Possible the formula was 'resurrected' from previous years but hard to confirm.
Here's my best guess after looking up some old materials.
F1 Mist Green is probably a lighter green than the earlier green. That earlier green was called Light Green Metallic and assigned a code of F3 in 1969. it was probably the same as the FF code paint in 1968.
Chrysler's system that started for two digit paint codes in 1969 was the first letter indicted the color family and the second how dark the color was. So F3 should be a little darker than F1.
When used as a three digit code, like JF1, the first letter designated the year (I think the year the color was introduced, but I didn't find the reference to decode that, which might indicate when the color was introduced).