This has come up a few times in the past,and i think the outcome was best to leave them "border-less",as,although it undeniably may look better,it's not an accurate depiction of the actual artwork,i.e,we had people saying "mine's the same,but has no black borders".
Also,people were tending to add them to not just white artwork,but pastel/light shades as well,and not always using black for the border,but using various shades of grey as well,so personally,i would go for the more accurate depiction,which is as they actually appear,but that's just one mans opinion of course;)
After seeing yesterday that somebody else had added a black border to white pages I thought I would look at some of my entries. This one in particular annoyed me because it just didn't look right on the page. I've added a black border to the pages and uploaded them again. If they are OK please replace my originals, if not, just delete