For all of the combinations that I just tried, the effect was quite subtle and so provided no interference in readability. For those wanting to see how their environment renders this effect, visit Reflections on “Higher Order Perl” §1.1 (why make people go searching for what you are talking about?).

The reason there is no added padding is because the shading difference is so subtle that none is required (not for me nor for the others who have contributed to this feature). If you have a level of padding that looks better in your environment, then you might want to donate the markup that produced it, since I have no way of testing anything in your environment (and I don't have a problem with the way things currently look, obviously) and if you provide "the code", then you are much more likely to get your desired change made (less work and less guesswork for the people that have to make the change), others can even try out your mark-up in their environment and provide feedback / alternatives.

If the shading isn't subtle enough, then you might want to note what CSS resulted in suitably subtle shading in your environment.

Thank you for providing the example so that other users can disable this feature for themselves if they so desire.

Why should the background be shaded just because I wanted it abstracted in the pages that display multiple nodes?

Yes, why should <readmore> have any visual indication at all? It was much funner when people would frequently wonder if they'd used the feature correctly because it seemed to have no effect at all. And the way it was done makes it so terribly hard to customize, as you discovered. :)

Actually, one of the most effective uses of the feature is when people view a node and worry that it is too long to be approved or front-paged or that they should consider it in hopes of having <readmore>s added. People who worry about that stuff very quickly learn that the subtle background change means "readmore" and so can judge immediately whether the node is appropriate to approve or front-page or consider.

Oh, I realized that I have my monitor gamma cranked down because I find the default settings make things rather whitewashed (to me) but testing with the default gamma settings makes the feature even more subtle, so the impact for readability of this feature is greater with my settings than it would normally be... Except in the "Dark theme". With default gamma in my environment, I would make the background change more subtle for the Dark theme.

But you don't appear to be using the Dark theme. So I'll wait to see if you provide more details and concrete suggestions. As to the one suggestion that was concrete, I see much more benefit in having the shading enabled by default (also because people who hate the effect usually have a much easier time adjusting or disabling it, as you did, compared to how easy it would be for people who don't see the feature to figure out how to enable it).