I beg to differ, the color shift occurs along the entirety of the panel line with the wing root fairing. The fairing only changes shape close to the wing itself, but joins the fuselage close to flush.
Walk up to one and touch it. They are multi-angled.
The panel (or panels) aft of the wing root fairing bends around the fuselage. The color shift you see is light-induced. The roundel section of the national insignia is reflecting light at a slightly different angle. That's why the dark blue has a non-identical hue.
The wing-root fairing on MISS RUTH is both light-shifting AND materially different (the latter on some Mustangs, not all).
Some Mustangs (again, not all) DO have a different color aluminum on that panel aft of the fairing. Some skip a panel. Some look identical.
As the plane ages the panel color differences moderate due to tarnish.
I see this on the bright work of my airplane every year after they're polished. Within a couple of months the shine goes from being like a mirror to dull like a coke can.
In shadow this Mustang appears gray, again due to tarnish. It wouldn't take long for the environment of Europe to tarnish the shine on an unpainted airplane.
Using restored warbirds is not always a reliable source. Only a handful come close to how they would have appeared during the war.
Another with the varied fuselage panel aft of the wingroot. I can find no explanation as to why some had this and others did not. I've found a half dozen variations on this.
Examples:
- Some match the fairing to the bright side.
- Some have a bright fairing, then--as we move aft--a panel that doesn't match, then a panel that matches the fairing.
- Some have a standard color fairing but skip TWO panels before a change (bottom).
- Some have all three the same color as the rest of the fuselage.
- Some have all three being different (below).
