My guess as to the color of the gear and wells, as well as the cockpit, would be one of the same interior greens as was used by Bell on P-39's and P-63's.
I have color shots only of the camoflaged Squirts, but after comparisons made between dozens of black and white shots of both Camo & NMF aircraft, it seems to me that interior green would be a logical choice for the gear and wells. Also, some shots of lineups of 412th FG birds show a mix of colored and what appears to be silver (or unpainted) gear struts.
The cockpit, almost without doubt, was interior green, with black instrument panel; the usual for birds of that era.
The wingwalks... I dunno for sure. I have a couple shots that seem to indicate two distinctive tones. Most others seem to indicate either dark grey or black. I think it may be safe to say that they were black (like many anti-skid walkways of the era) and may have faded and changed appearance with time and wear, ie; I'd paint them a faded dark grey.
Hope this helps and doesn't hinder!
Fade to Black...