I figured out how to change the actual content of the WP error messages ( http://blog.cyberquill.com/wp-comments-post.php ), and now I'd like to customize the design of the error page, specifically to get rid of the light green background and to change the page title from WordPress>Error to something else.
Does anybody know what file the error page template is located in? I can't find it.
PS: The link I posted above doesn't seem to work. Sorry about that. Apparently the page only loads by visiting my blog and actually making an error that prompts an error message, even though the URL is identical. It's all very mysterious. In any case, I think my question is clear even without looking at the page.
Found it. The error page can be customized in install.css, located in the admin css folder.