Try going to the BBC homepage, then click a link in on of those pastel boxes. Once that’s done and it’s gone to the new page, go Back and do it again. Repeat this several times. You should notice that the box gets darker over time. It’s intended to indicate subtlely which sections you frequent and effectively ‘wears a path’ over time. I rather like it.
The reason I found this is that I was searching through Google trying to find out which CMS the BBC use, and ended up on a few blogs discussing it. Although I knew about it before seeing it again reminded me to post it here.