This is an attempt to overcome the impasse over at Accessibility improvements for vertical tabs.
As I have already stated elsewhere the general problem with regard to accessibility and usability is that one size doesn't fit all.
So we should make some of the accessibility improvements more configurable. One way which even allows for configuration on an individual user level is a separate theme for accessibility settings.
I have created a Zen sub-theme which allows setting some options which affect the visual appearance of the Drupal site. This is only a very first stab and more of a proof of concept, though.
(Note: I had to add an additional file extension to the zip-file for attaching the theme to this post.)