This is amazing info, my friend @wkubacki!
I will surely use it!

Thank you everyone for these very detailed responses about the various colors. I too have learned a lot from this, and I will definitely be taking some notes here.

John, @johnb

I realized that I never gave you an answer to your question about the color you posted. I think that the others have done so. As they have stated, this area was covered under plexi glass, and I'm sure the sunlight would have faded this area at a faster rate than other locations like the cowling. Blue Black would fade into a dark gray color that had a bluish tint to it. It would get lighter and the blue color would become more evident as time went on.

I think you are good to go for these reasons. I don't think anyone could prove otherwise. In the end, it's your model, and as long as you are happy with it, that is all that matters. I personally believe it looks perfect "as is" right now. I wouldn't change a thing.

Keep it going my friends ! This is some really good stuff ...

Woody, @wkubacki
Maybe one of these days I will continue on with the project. It takes a lot of time to put it all together.

This is what I have found so far by netting, my friend @johnb:

1. First, from the definitive j-aircraft site:

https://j-aircraft.com/research/gregspringer/radios/radio_systems.htm

where you can read:

The directional loop antenna was mounted in the fuselage deck beneath the canopy behind the rollover pylon. It consisted of two round stamped-metal frames with a center post. The actual antenna was made of insulated wire wrapped around and between the frames. Cloth was then applied over the wire and doped. This gave the assembly the appearance of a thick loop with a center post. The photo-etched ‘twin loop antenna’ found in many aftermarket detail sets today is in fact only the support frames which survived after the cloth and antenna wire disintegrated. These frames are seen in a number of restored aircraft that no doubt led to the error. Credit goes to Ryan Toews and James Long for discovering this fact. The drive motor for rotating the loop antenna is contained in a box inside the fuselage just below the antenna and the large central unit for processing the radio signals was housed in the rear fuselage behind the rear cockpit bulkhead.

2. A review of the Tamiya 1/48 A6M2 Zero by Nicolai Plesberg...

https://modelingmadness.com/review/axis/j/jnaf/plesa6m2.htm

where you can read:To finish the cockpit, the headrest and DF loop was painted red brown (Humbrol 160), while the antenna mast went natural wood (Humbrol 110)...

...

3. Third, a great discussion at Hyperscale.com...

https://www.tapatalk.com/groups/hyperscale/color-of-a6m5-antenna-masts-t211845.html

...in which you may see these pics:

Hope this helps you determining which color you may paint your loop.

Preparing for paintwork

Before starting the scheme paintwork I started with painting the wheel wells and canopy first.
Wheel wells metallic blue green according the manual.

Stay safe

One of the best time in building models comes : painting !
John , I am waiting impatiently for the next stages , you have a very studied work so far , well done !

Nice painting step, my friend @johnb!

Thanks my friend @gblair!