The clsoest to tht green color is tamiya OD wtih gloss sprayed over it. Darkens it up, but its a tad to green just a by a smidge to be accurate, but I like it.

Testors OD 34087 oversprayed with gloss is very popular and my first choice, but its very different color from your stock tank.

I reccomend you paint the entire tank. So it all matches. Then do any kind of shading and. Weathering to highlight or darken.