Edit in JSFiddle

$(function() {
    $.fn.extend({
        kirmizi: function() {
            return this.each(function () {
                this.style.color = "red";
            });
        },
        mavi : function() {
            return this.each(function() {
                this.style.color = "blue";
            });
        },
        yesil: function() {
            return this.each(function() {
                this.style.color = "green";
            });
        }
    });
    $("#List li:lt(3)").kirmizi();
    $("#List li:gt(2)").mavi();
    $("#List li:eq(2)").yesil();
});

<ul id="List">
    <li>1</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
    <li>5</li>
</ul>