Sean asks: I came across your Blog by pure chance I was looking for information about a replacement product for colron wood dye, for use on plastic stone kits any info would be a great help.
I'm not actually sure what Colron wood dye is supposed to do. It's a name that I know from very old model railway magazines, but I don't own a can myself.
(Incidentally, Colron still make it)
At a guess, the dye is painted onto the stone to add colour, especially in the mortar joints.
If I'm right then there is a readily available product that also does this - Citadel Agrax Earthshade. You can buy it from any Games Workshop.
An acrylic wash, you can paint it on anything that needs brown stuff in the nooks and crannies.
My experiment is on a sheet of Wills stonework. I've painted it with Humbrol 121 and picked out a few stones in variations on this. Once dry, aided by a dust of talcum powder, the Earthshade is washed over everything.
I think the results are a bit brown. Perhaps a few drops of black wash (Nulin Oil) would help. A final dry-brush with 121 would help too.