Hello Attiyah.
I had already googled 'midnight sun' before replying the first time, and have seen many relevant photographs. Particularly at this site, which one can sift through and find hundreds, if not thousands, of photos from the North Pole.
On the NOAA site one can choose the time and date range for photos (actually they're camera stills) from 2002 to the present. For the date, I chose January 2004 to September 2004 (to bracket the summer solstice in June), with the 'all times' option. If the sky was relatively free of clouds, and the camera wasn't blocked by ice or snow, I could clearly see a blue background sky. Some were brighter than others, but still blue.
The Scandinavian 'midnight sun' photo that you linked to does show a "dusky" blue sky as well.
Sorry, I'd write more but it's late!
Just this: I think there's some energy considerations re: energetic solar particles incedent upon the earth's atmosphere during a "normal" aurora and the requirements for a "global" aurora that would have to scatter light throughout the atmosphere. I'll think about it more. I'm a little foggy right now; time to sleep.
Oh, could you please list the references for the spectral data you included in your first post's introduction?
Thanks,
SMEaton