Guys,
I don't know if I have done this right but it works. I've added a new template in  '/etc/e-smith/templates/home/httpd/html/horde/imp/config' called 480legend
I did this because the legend section as shown below did not exist in my prefs.php or in any original template.
// show mailbox legend? 
// a value of 0 =no, 1 = yes 
$_prefs['show_legend'] = array( 
    'value' => 1, 
    'locked' => false, 
    'shared' => false, 
    'type' => 'checkbox', 
    'desc' => _("Show legend in the mailbox view.") 
Then I added 'show_legend' in the original 180display template located in '/etc/e-smith/templates/home/httpd/html/horde/imp/config' at the line 'members' as shown below. This item was also missing
$prefGroups['display'] = array(
    'column' => _("Other Options"),
    'label' => _("Display Options"),
    'desc' => _("Change display options such as how many messages you see on each page and how messages are sorted."),
    'members' => array('sortby', 'sortdir', 'max_msgs', 'num_words',
                       'nav_expanded', 'show_legend')
Finally I expanded the templates: /sbin/e-smith/expand-template /home/httpd/html/horde/imp/config/prefs.php
It works now, but have I done this right?
Regards,
Peter