Nice pics there Peter. I would think the easiest way to replicate the darker shade around the cockpit would be to paint the aircraft overall, and then roughly mask off, leaving the area around the cockpit free, and either spray or brush, varying the weight at the edges slightly, in the 'real' shade of the colour.
Not sure about the gun-muzzle tape colours, but certainly in Europe, this was done using doped fabric patches. The fabric was a sort of brown / buff colour, sealed in place with a red coloured dope, which, when dried, gave a dull, red/brown appearance. This was where the muzzles were inside the wing, with a gun port, as per Spitfire, Hurricane, Beaufighter etc.
Where muzzles protruded, eg Mustang, the cannons on Hurricane IIC etc, AFAIK, the tape was applied over the muzzle and sealed around the edges, and appereared more of a brown colour, like a buff, manilla envelope looks, with a hint of pale red, the latter, I presume, being the streaks of dope. Logic tells me that something like ordinary masking tape might have been used, or the type of tape we now know as 'Duct' tape or 'Tank' tape which, then, was made from a cloth fibre weave, and was similar in colour to modern-day masking tape, perhaps with a slight greyish tinge.