Hi SUNGOD, I'd say very much like the original Enterprise filming miniature: light grey with a hint of green -- seeming THE INVADERS saucer was made at the same shop too. The green was added to improve the models definition from the blue screens which were used then (Now green is the preferred color for screening, so if you're planning on keying it, may want to add a hint of blue instead, lol). The lighter grays could also be lit without many issues. Here's a bit of info on the Enterprise one:
Thanks for that and I might well be painting over the silver on mine. Be good as I have a few saucers in silver so it'll add variety.