Background Image Switch Javascript Works in Firefox & MSIE. But not in Chrome

Question

My JavaScript code works in Firefox & MSIE. But not in Chrome. In FF or MSIE, the "saved" button works, changes background image when I reload. But in Chrome, the "saved" button does nothing. And there's no error message in Chrome Inspector. "Reload" button works in Chrome though.

var skin = "";
var myRegExp = /;/g;

if (skin == "blue") {
  document.body.background = "blue.jpeg"
} else if (skin == "green") {
  document.body.background = "green.jpeg"
}

function setCookie() {
  skin = document.f.s.value;
  if (skin == 'blue' || skin == 'green') {
    document.cookie = "skin=" + skin + ';expires=' + expireDate.toGMTString();
  } else {
    alert('Not Valid Skin Color');
  }
}

<form name="f">
  Change Skin to:
  <input type="text" name="s" /> <br> Colors include: blue, green<br>
  <input type="button" name="saved" value="Save" onclick="setCookie()">
  <input type="button" name="reload" value="Reload" onclick="location.reload()">
</form>