zend-framework2 - ZF2 Capturing HeadStyle Helper

Question

I have used the following codes in my app.

<?php $this->headStyle()->captureStart() ?>
body {
    background-color: <?php echo $this->bgColor ?>;
}
<?php $this->headStyle()->captureEnd() ?>

I'm getting this error in my view script.

Fatal error: Call to a member function captureStart() on a non-object.

What's wrong?