Since it all started from a photo we have published (and that we own), I guess I may have a few comments.
Just to add a bit more of uncertainty to the whole matter, I would like to note that such was the lighting (cloudy and hazy late winter day) and the position of the underwing Balkenkreuze, that I would prefer to have at least a second shot before confirming that such marking is in reality devoid of the interior white, and that this is not one of the many visual illusions we have all found sooner or later during our researches...
Unfortunately there isn't a "second shot", of course, so I guess that we should remain with the doubt.
At any rate, here is a detail of what is visible in the photo and Klemchen refers to...
It would also be nice to know - if possible - the precise reference of the photographs which Klemchen affirms are supplying even better examples of the absence of the white in the underwing Balkenkreuzen (I suppose on other Bf 109s...).
TIA