It is impossible to replicate the original Grello formula as typically mixed by Fat.
Doug's understanding is partly correct as I'm sure the info passed on to him was.
The color was achieved by using flouro powders to tint layers of clear. The powdered pigment product, made by Radiance Inc. out of California, was quite popular during that time period. The powder would be measured out and added to the liquid clear, mixed, then sprayed. The company ceased production of the powders 10 years ago.
Although I've still got some of the yellow pigment, I've been unsuccessful in finding the green again
cheers,
rody