I,m just getting back to moddeling after about 20ish years, but who's counting

So I went onto ebay and bought a 1/35 Bmw r75 + sidecar and made a start but it quickly became clear that some painting would be required before assembly. I want to portray this as an early production european version, so which grey do I use? I have easy access to a supply of Humbrol paints,, one of which is called matt tank grey, however the Tamiya recommendation of "field grey" equates to a green in the Humbrol range...can anyone help...

This is a great site BTW
Cheers David