The colors you are referring to suggest a similarity to the curent paint being worn by the Italer F-16 B/D Viper. Yeah, yeah, i know you are loking at an older plane, but the colors sound liek they match. Try this:
The grey underside is possibly FS 36375 (Light Ghost Grey). The green is FS 34227 (ModelMaster 1716, Pale Green). The pale tan is ModelMaster 1567 (Flat Tan, no FS number). Hope that helps.
Mike
Sua Sponte