<p>Anyone know a simple method to swap the background color of a webpage using JavaScript?</p>

Modify the JavaScript property
```
document.body.style.background
```
.
For example:
```
```
function changeBackground(color) {
   document.body.style.background = color;
}

window.addEventListener("load",function() { changeBackground('red') });
```
```
Note: this does depend a bit on how your page is put together, for example if you're using a DIV container with a different background colour you will need to modify the background colour of that instead of the document body.