Wouldn't be too concerned about the colour - the official 4B0 colour was only approximately adhered to by the factories - the priority was to crank out huge numbers of vehicles.
You can often retrieve nearly the original colours if you rebalance the scans with Gimp or Photoshop - there have been threads on this in the past. This article -
How to clean up a scanned image: engravings has some useful techniques.
Regards,
Charlie