If you are using the 'flat' theme then copy the file modules/mod_jevents_cal/tmpl/flat/calendar.php to templates/YOURTEMPLATE/html/mod_jevents_cal/flat/calendar.php
Then find the code
case "prior" :
case "following" :
$content .= "<td class='flatcal_othermonth'/>\n";
break;
at line c. 190 (line number will vary based on the theme you use as will the $content line
and replace it with
case "prior" :
case "following" :
$dayOfWeek = JevDate::strftime("%w", $currentDay ["cellDate"]);
$class = ($currentDay ["today"]) ? "flatcal_todaycell" : "flatcal_daycell";
$linkclass = "flatcal_daylink";
if ($dayOfWeek == 0 && !$currentDay ["today"])
{
$class = "flatcal_sundaycell";
$linkclass = "flatcal_sundaylink";
}
$link = $this->htmlLinkCloaking($currentDay["link"], $currentDay['d'], array('class' => $linkclass, 'title' => JText::_('JEV_CLICK_TOSWITCH_DAY')));
$content .= "<td class='flatcal_othermonth'> $link</td>\n";
break;
The code you need to use will vary by theme too but hopefully that is enough to get you started