改变select下拉框中对应option的样式颜色已经展示的option如何进行颜色对应

var checkIndex = $("#selCate").get(0).selectedIndex;

    for (var i = 0; i < $("#selCate option").size() ; i++) {

        var checkvalue = parseInt($("#selCateNone option")[checkIndex].value);

        if (checkvalue < 0) {

            $("#selCate").get(0).style.color = "red";

        } else {

            $("#selCate").get(0).style.color = "black";

        }

        if (parseInt($("#selCateNone option")[i].value) < 0) {

            $("#selCate option")[i].style.color = "red";

        } else {

            $("#selCate option")[i].style.color = "black";

        }

    }