As far as I know, none of the Fiberglass versions was painted. Slight differences in molding made them different shades of olive drab or olive green. The props where also heavily weathered with dust and "bug-blood".
Paints like Model Master 2112 or the Humbrol 117 are "close" but you will probably need to mix them with other colours of the same line to make the colour you imagine it to be.
Going with a slightly Satin paint will make it reflect more light and might make it appear to change colours between grey-ish green and green-ish grey, as they did in the film.
