Changing background color of text box input not working when empty

I am having a tough time with this javascript code to change the background color of a text input if the input is empty.

Here is the code:

function checkFilled() {
    var inputVal = document.getElementById("subEmail").value;
    if (inputVal == "") {
        inputVal.style.backgroundColor = "yellow";
                }
        }

Example: http://jsfiddle.net/2Xgfr/

I would expect the textbox to come out yellow at the beginning.