I forgot about the yellow wing tips, which I noticed in photos in a couple of other books. I believe this was on the underside of the wings only, not on the upper surfaces.
Yes, the aircraft in the b&W photo is probably one of Oesau's two '109Fs, and I posted it just to show the demarcation of the colours on the spinner.
That's Oesau, second from right, in the light-coloured jacket, with Pflanz, Leie and Mayer, when they'd been awarded the Knight's Cross. I cropped the photo, missing one of the quartet, in the one I posted, which is one from a series taken at the same time.
Yes, blue is a Geschwader Stab colour (Gruppe Stab being green), and although it does seem to be a somewhat unusual (spinner) colour for a fighter unit, being more associated with bomber and Bf110 units, it is in line with the Geschwader Stab roles of Oesau, Pflanz, et al.
In the version of the photo I posted (different to the one posted by Steve) , if that is blue, then it looks rather lighter than one would expect, presumably a result of exposure during reproduction and the (book) printing process.
However, I have seen this same series of pics in a number of other publications, with at least one from a slightly different angle, where the 'blue' definitely looks darker, appearing as one would expect that shade of blue to appear in a good monochrome photo, just as it does in the first pic, of Wurmheller, posted by Steve.
I'll see if I can find some more info or pics, as I'm fairly sure I've seen reference to Seeger, possibly with a photo, somewhere.
Can't promise when I can post anything - if I find anything, but I'll try.