Change the back round color of a date field in crm 2011

I have the following line of code that I would like to use to change the backround color of a date field.  It works on a value field but on a date field it only changes the backround color around the date picker box.  Does anyone know how to fix this?

document.getElementById("po_facevalueoflifeinsurancepolicy").style.backgroundColor = "red";

Also, to set it back to the normal color do I just set it back to "white" or is there a better way to handle it?

Thanks, Dale