What do the colors mean?
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
Sourcecode is here.
Another cool discovery this evening was Gliffy, an online flowchart and diagram maker. Drawing was easy. Something seems screwed up in exporting; I notified their customer support. A very nifty little ap.