I don't think that the rectangle on the leading edge has to do with a ladder.
I think that there is another color under the white line over the wings fillet, but I can't say if it's red, It just looks lighter than the nose and tail.
Regards
Massimo
Have to disagree with you on this part I think the white lines may be bare metal of the aircraft skin from the the ladder rubbing the leading edge or maybe some kind of light colour primer?
If you look at the other picture I have posted you can see the same pattern only not as prevalent. Maybe less ware & tear at this point in time but is clearly wear of the finish coat of paint.
On Nelsons plane the pattern is more prevalent as well as beyond the landing gear nacelle. Wish it was clearer I think it would show the wear better.
Now if you look at the ladder picture you can see that there is two forms at the end of the ladder that are cut to fit the profile of the leading edge of the wing. You can actually see the gap between the two cut forms. Those forms are what I think is forming the two horizontal lines of the rectangle when the ladder has been dragged across the wing face.
All open for debate of course.
The new pictures do prove a few facts as you mentioned & a few I noticed as well. The white line that runs up & over the wing is with out question there & now we know exactly wear it ends interestingly flush with the most outer edge of the wing radius. The darker nose colour continues beyond & lower than the end of the white stripe & I would not of thought it would be like that. Also you can just catch a glimpse of the dark wing radius colour & its demarcation line to what ever the top of the wing colour is.
I kind of cropped it a little close.
When you look at the still in the video it is a little more obvious.
What ever that dark wing radius colour is I think it is the same colour that is along the leading edge of the wing & forming the patterns around the landing gear nacelles as well.
I really do think that these new pictures are frames from a news reel though. Some where maybe there is actual motion film of this plane. That would be very exciting to find.
Edit: Just noticed that one of the older profiles has the stripes on the prop not one but two & looking at those new pictures closer I think there is two as well.