First you need to put the Input variable into the HTML (between the <body> tags), so that you can see the output of the script.
Then you only have to add CSS styling rules for the different kinds of highlighted syntax (keywords, strings, numbers...) in order to actually get different colors. You can find a bunch of themes for use with pygments on GitHub.
Here's a complete sample workflow:
http://www.editorial-workflows.com/workflow/5249622561783808/DObDwB-OfUI