Try using $this->baseurl
and $this->template
, like so:
JHtml::_('script', $this->baseurl . '/templates/' . $this->template . '/js/override.js');
Try also wrapping your jQuery code in document ready as shown below:
jQuery(document).ready(function(){
jQuery('#sp-feature-wrapper').css('background', '');
});
Note that you also missed out a '
before background
in your code which I've added in for you.