Ah! Well, there are many different types of “sitemaps”. Yours is very attractive and serves it’s intended purpose quite well. Most of the “autogenerators” out there that I have seen are more oriented toward providing enhanced indexing than they are for “summarizing structure” and therefore, out of the box, would most likely give you a lot more links than you want.
One that looks like it might be easily modifiable to create a textual version of what you want can be found in this article titled “Use an XHTML Sitemap for Better Indexing”. Note that if you read through the comments that follow the article, you will see a link to the WordPress Codex where you can see how to “decrease” the level of detail the generator produces.
That might give you a good start; you can always “prettify it” with CSS to produce the colored boxes if you want, or just wrap the output in a WordPress “page”, so the text is surrounded by your “look and feel.”