Create an advance theme as described here and then copy the function "a_count" in qa-theme-base in your qa-theme.php. If $post['answers_raw'] == 0, you can insert a different style that you will then color in your css. Something like that should do:
$style=null;
if ($post['answers_raw'] == 0)
$style='qa-a-count-none';
else if ( @$post['answer_selected'])
$style='qa-a-count-selected';
$this->output_split(@$post['answers'], 'qa-a-count', 'SPAN', 'SPAN', $style);