After fiddling around with various TAMIYA colors, I painted my "B" type S-Tank in a mixture of about 70 per cent XF-22 (RLM Grey) and 30 per cent XF-58 (Olive Green).
On the model, this came out looking like a weathered grey with a distinct green "undertone." I was trying to match the shade of a real S-tank in a color photo, and I'm happy with the result.