I can help here. A few years ago I accidentally dropped a heavy object on my Rogue Studios painted Natty MSH1 helmet so to touch it up I took it to the local model shop and compared Tamiya paints.
Id say look in to humbrol paints they have a much more extensive range , thou they are enamels, but if you are using spray paint tamiyas then there is Field greay, it looks right if on the helmet but it is actually alot lighter than it should be,
Ipersonally think the olive is to olive, Id try Nato green if Iwere you , it looks pretty close to floquil POG , or even mix field grey with Nato green, if you are air brushing , but if you are using spray cans go feild grey