input.not(li.tagit-new >input) {
background-color: lightgrey;
}
<ul id="tagAdministrator" style="width: 505px" class="tagit ui-widget ui-widget-content ui-corner-all">
<li class="tagit-new" style="box-shadow: none;">
<input type="text" class="ui-widget-content ui-autocomplete-input" autocomplete="off">//css should not be applied to this
</li>
</ul>
<input type="text" class="ui-widget-content ui-autocomplete-input" autocomplete="off"> //css should be applied to this