Hi there.
When I was making my K.9, I was obsessing about the colour myself.
Tony farrell suggested I contact Matt Irvine himself.
He very kindly sent me a reply which can be found in my K9 build diary here:
https://tardisbuilders.com/index.php?topic=10368.105
Ironically, in the end, I just went for Wilcos metallic grey spray paint as it was the cheapest I could find!
Hope that helps.
Russell