original:
$blackLine = $conf['line'] ? '<img src="clear.gif" width="1" height="' . intval($conf['line']) . '" alt="" title="" /><br /><table border="0" cellpadding="0" cellspacing="0" width="100%" bgcolor="black" style="border: 0px;" summary=""><tr style="border: 0px;"><td style="border: 0px;"><img src="clear.gif" width="1" height="1" alt="" title="" /></td></tr></table><br />' : '';

new:
$blackLine = $conf['line'] ? '<table border="0" cellpadding="0" cellspacing="0" width="100%" style="background-color: #abbbb4; border: 0px; height: 1px;" summary=""><tr style="border: 0px;"><td style="border: 0px;"></td></tr></table><br />' : '';

$blackLine = $conf['line'] ? '<img src="clear.gif" width="1" height="' . intval($conf['line']) . '" alt="" title="" /><br /><table border="0" cellpadding="0" cellspacing="0" width="100%" bgcolor="black" style="border: 0px;" summary=""><tr style="border: 0px;"><td style="border: 0px;"><img src="clear.gif" width="1" height="1" alt="" title="" /></td></tr></table><br />' : '';

http://blog.exites.de/2011/04/typo3-adminpanel-gibt-unschone-schwarze-tabellen-aus/

Da hilft nur: Quick&Dirty Code-Änderung

Öffne die Datei /typo3/sysext/feedit/class.tx_feedit_editpanel.php und suche folgenden Abschnitt:

FE Edit: Hide black border

TYPO3