I think I get you now, you need to reset the background colour in your jQuery:
$(document).ready(function ($) {
$('#accordion').find('.accordion-toggle').click(function () {
//stop us reusing $(this) as it's not efficent
var $this = $(this);
//First things first, reset all the accordion's colours back to default
$("#accordion .accordion-toggle").css('background-color', '#E4E4E4');
//Expand or collapse this panel
$this.next().slideToggle('fast');
//now set only the correct one to the new colour
$this.css( "background-color", "#191970" );
//Hide the other panels
$(".accordion-content").not($this.next()).slideUp('fast');
});
});