Reading up on rat genetics
it appears only the black rat was in the British Isles by the first century (spread by Roman traders)So for what it's worth I am going to pick up on this and choose a base color of Vallejo Game Color 72.050 Cold Grey, (a few drops shaded with 72.051 Black, and highlighted with 72.001 Dead White).
I've brush primed with Vallejo 72.600 White Primer
It may be too dark, but we'll give it a shot.
I may end up going with brown rats if it doesn't work out.
