Look for the case "date": inside the function get_field_correct_displaying. You can add your style info inside the else statement (in bold):
[pre]
case "date":
$field_value = htmlspecialchars($field_value);
if ($field_value != '0000-00-00 00:00:00' && $field_value != '0000-00-00'){
$field_to_display = format_date($field_value);
} // end if
else{
$field_to_display = "<i style="width:100%;background-color:#FF0000;"> </i>";
} // end else
break;
[/pre]
What that should do is color the cell red (with the width set to 100% of the container).
If it doesn't look exactly the way you want it to, you can modify the style.