Visual diff for updated posts in RSS reader

I’m an RSS addict. If I follow your site, and you’ve got RSS, that’s how I do it.

I like that RSS can tell me when a post is updated. Unfortunately, sometimes it’s not clear to me what was changed: was new information added? Was whitespace added? Just copyediting? It would be great if I had an RSS reader that could show me what changed, with two side-by-side views and color coding. Or even just highlighting the edited parts in red.

For RSS readers that cache lots of content, this should be easy to implement, and would save a lot of brainpower on my part…