jQuery(function($){ $(window).scroll(function() { // selectors var $window = $(window), $body = $('body'), $panel = $('.panel'); // Change 33% earlier than scroll position so colour is there when you arrive. var scroll = $window.scrollTop() + ($window.height() / 3); $panel.each(function () { var $this = $(this); // if position is within range of this panel. // So position of (position of top of div <= scroll position) && (position of bottom of div> scroll position). // Remember we set the scroll to 33% earlier in scroll var. if ($this.position().top <= scroll && $this.position().top + $this.height()> scroll) { // Remove all classes on body with color- $body.removeClass(function (index, css) { return (css.match (/(^|\s)color-\S+/g) || []).join(' '); }); // Add class of currently active div $body.addClass('color-' + $(this).data('color')); } }); }).scroll(); });]]>