I've been using the white theme since I've been here. Its actually more of a light blue though.
Its not because its "brighter", but because tt has far less contrast, so there are no bright surprises when browsing the photos at night. The decreased contrast also keeps brightly colored objects (white lettering, photos) from burning images into my retinas by the time I scroll down - I don't get the white letters "ghosting" into the black background of my sight when I look into the background.
That's why I use the lighter theme - don't know why I would be the only one using it. Its a very clean appearance after all. I recommend people try for a couple days if you haven't already.