is_category for Custom Field

In index.php, I’m calling specific Custom Fields for specific Categories only. The second half of the below code works fine (at displaying the ‘Feedback’). The first part however, does not work fine (at displaying ‘Feedback’ only if the parent category ‘Singles’ is being displayed from. Is the first part right/completely wrong/slightly there?

<?php

is_category('Singles');
if ($is_category=="Singles") 

$values = get_post_custom_values("Feedback");
if(!empty($values)) {
    $feedback = "Feedback";
    echo $feedback . $values[0] . '<br />' . '<br />';
}   ?>

Cheers