Cockpit interior paint

Without wishing to get into a massive discussion about the exact colours used and what they look like when photographed, can anyone enlighten me why for If we take as an example a Spitfire.
In many photos the interior cockpit walls and frames are painted green. Not the camouflage green colour. Why not black and why paint at all? I can see that to protect the metal it would be primed then painted but inside the rear fuselage the colour can be silver (or bare metal). On aircraft that are scratched inside the bare metal seems to show through rather than a primer. (or is the primer clear?)