Comment 13 for bug 517777

I'm also having this issue, Dell Mini 9 with the standard Dell Hardy Heron distribution, didn't always do it, noticed it a few months ago - so probably about the time MichaelN reported it. It *is* annoying (ie, I can see why he's annoyed).
may to be something to do with something called RGBA, see this thread http://ubuntuforums.org/showthread.php?t=1435575&highlight=nautilus+background+color+change
Sorry I can't provide more info, and thanks for the workaround.