The designer uses colors to indicate different information.
"blue: for links (the A tag)
red: for tables (TABLE, TR and TD tags)
green: for the DIV tag
violet: for images (the IMG tag)
yellow: for forms (FORM, INPUT, TEXTAREA, SELECT and OPTION tags)
orange: for linebreaks and blockquotes (BR, P, and BLOCKQUOTE tags)
black: the HTML tag, the root node
gray: all other tags (quote from http://www.aharef.info/2006/05/websites_as_graphs.htm)"
this is new way to experience a website literally 'visually.'For example, this is a graph version of msn.com

Try it yourself
More info