There's definitely some interesting things going on with human reasoning in the way different people interpret the result. I originally assumed the images would average to gray, but when I think about it logically, that would be kind of miraculous. We wouldn't expect a bunch of photos taken on Mars to average to gray (to be perfectly balanced in R, G and B), so why did I expect photos taken on Earth to? It would mean all the colors are in a very precise balance, which would be kind of odd.

With random images which include a few outdoor photos, there is a noticeable effect from the sky, but not as dramatic as I might expect - it tends to produce a whitening, rather than a visible blue.