On front coil springs white is normally IMHO an identification mark but an over or under the measured limit mark - allowing the installer to use two with the mark or without to better match a pair. In later years the white was applied using a different method than the identification marks but in 66 it would stiff be a brush
As far as the mint green I've currently have nothing to compare to (without using the service replacement parts list printed years later0) Sorry
Have single green examples used on SOME 6cyl applications