After some experimentation I have managed to get a pretty decent match to the elusive Humbrol 170 AKA Brown Bess with Tamiya acrylics.
humbrol on top, tamiya on the bottom.
tamiya on top of Humbrol APC:
Paints are Tamiya XF-51 Khaki Drab and XF-7 Flat Red. I added 3ml of XF-7 (flat red) measured with a syringe to 10 ml bottle of XF-51. The only problem is I was incrementally adding 0.5ml red between resprays to home in on a match so I suspect the ratio is closer to 3.5ml red (maybe even 4) to 10ml khaki drab. It was airbrushed thinned with tamiya acrylic thinners (which is isopropyl alcohol). Also it looked much redder when the paint was wet. I though I had it at 2ml of red but it was still too green.
I'll double check the ratios with a fresh pot of Khaki on the weekend but this is the closest I've managed to get (both visually and photographically).
disclaimer: just because this is working for me doesn't mean it'll work for anyone else. BB looks slightly different depending on how it's applied but I specifically need a paint matched to this APC for a larger item in the same scale.
