dynamic row style linked to the custom row background property

I try for dynamic colors of my rows when onRowDoubleClicked but not changed why?
[Quote]
ogrid.onRowDoubleClicked = function(event, rowIndex){
ogrid.defineRowProperty("background", function(row){
var value=length(this.getCellText(2, iRow));
return value>13 ? "#b0e0e6":"#FFFFCC" ;
});

ogrid.getRowTemplate().setStyle("background", function(){
return this.getRowProperty("background");
});

ogrid.refresh();
}
[/Quote]