I'm a massive fan of using the particular monk's CSS to determine the hilighting... and providing a seperate option to enable it. (disabled by default)

Perhaps also providing a couple of default styles to get you started, a nice light-on-dark, a dark-on-light etc

even if it was just based on css, without an off switch

 .codeblock { 
    background-color: inherit!important;
    color:inherit!important;
}
[download]

and boom, the hilighting disappears... and it starts looking like normal text (black on white) Or you could even do something outragious and provide a real user stylesheet to your browser to over-ride these things...