设置DataGrid单元格的颜色

<mx:DataGridColumn headerText="变更终验剩余工期" dataField="realdateChangeFinalcheck" labelFunction="getDays">
       <mx:itemRenderer>
                            <mx:Component>
                                <mx:Label>
                                    <mx:Script>
                                   
                                        <![CDATA[
                                            override public function set data(value:Object):void{
                                                super.data = value;
                                               if((value.realdateChangeFinalcheck as Date) != null && value.realdateChangeFinalcheck < new Date()){
                                                    this.setStyle("color","red");
                                                }else{
                                                    this.setStyle("color","black");
                                                }                
                                            }
                                       
                                        ]]>
                                       
                                    </mx:Script>
                                </mx:Label>
                            </mx:Component>
                          </mx:itemRenderer>
</mx:DataGridColumn>

<mx:DataGridColumn headerText="销售项目编号" dataField="projectNo" />
在第一个DataGridColumn中，实现的功能是当剩余时间为零或零以下时以红色显示。
下面是getDays方法：
/*计算到期时间距离当前时间的差距*/
private function getDays(item:Object,column:DataGridColumn):String{
if(item[column.dataField] == null){
return "";
}else{
var date1:Date = new Date();
var date2:Date = item[column.dataField];
var df:DateFormatter = new DateFormatter();
df.formatString = "YYYY-MM-DD";
date1 = DateField.stringToDate(df.format(date1),"YYYY-MM-DD");

var num1:Number = date1.valueOf();
var num2:Number = date2.valueOf();
var dif:Number = num2 -num1;

var days:Number = dif/24/60/60/1000;
return days;
}