for everybody that maybe need the answer, here is my solution:
var RownumFontColor = “red”;
var HeaderFontColor = “yellow”;
var HeaderBackgroundColor = “brown”;
$(“.jqgrid-rownum”).each(function() { this.style.color = RownumFontColor; });
$(“.ui-jqgrid-sortable”).each(function() {
this.style.color = HeaderFontColor;
this.style.backgroundColor = HeaderBackgroundColor;
});