Wish I Could...

Yeah if I recall when I did that test print of the loco body it was in that translucent resin purely because that is what I had in the printer at the time it wasn't by design.  I'm not sure if you can buy Brown, but you can definitely dye it as you can use any of the colour inks used for mixing with the normal poured 2 part resin liquids.  I've got come of those pigments, but not yet tried them.  White may be a problem if you are using it with a clear resin though as you would need to make it opaque as well.  Why he/she doesn't just buy a bottle of white resin I don't know that is freely available