Seeing as you're a Thunderbird user, you might be interested in the following tip to emphasise quoting by setting increasingly dark backgrounds for the quoted levels in addition to the usual colour bars in the margin.
Add the following
blockquote[type=cite] { color: navy !important; background-color: RGB(245,245,245) !important; border-right: 0px !important; } blockquote[type=cite] blockquote { color: maroon !important; background-color: RGB(235,235,235) !important; border-right: 0px !important; } blockquote[type=cite] blockquote blockquote { color: green !important; background-color: RGB(225,225,225) !important; border-right: 0px !important; } blockquote[type=cite] blockquote blockquote blockquote { color: purple !important; background-color: RGB(215,215,215) !important; border-right: 0px !important; } blockquote[type=cite] blockquote blockquote blockquote blockquote { color: teal !important; background-color: RGB(205,205,205) !important; border-right: 0px !important; }
to your %APPDATA%\Thunderbird\Profiles\Default\xxxxxxxx.slt\Chrome\UserContent.css file.
Note that %APPDATA% will usually be C:\Documents and Settings\YourName, and xxxxxxxx is a random string.