[jaywilliams+]

The easiest way would be to add some inline css into the page header, like so:

<style type="text/css" media="screen">
body{
	background-color: <HARMONIOUS_DARK>;
	color: <HARMONIOUS_BRIGHT>;
}
</style>

You could set all of the nitty-gritty info in an external css file.
Just use the inline for colors only.