Because it’s not an officially released theme (yet) you have to check it out via the subversion repository, but that’s a pretty simple call to svn co http://svn.automattic.com/wpcom-themes/monotone/

Here’s a snapshot of the post page, with background colour pulled automagically from the photograph:

And, the archives page with date selector:

Thanks to Weblog Tools Collection for the tip, and Automattic for creating the theme!

Update: The monotone theme uses a function called image_scrape() which does some cool stuff for the post display on the web, but had the nasty side effect of yanking images from the RSS feed. I fixed my copy of functions.php to avoid the problem, and allow full images in the feed. Here is my trivial modification to the image_scrape() function:

// remove image tag from post_content for display
function image_scrape($entry) {
	// don't scrape the image for the feed
	if (is_feed()) { return $entry; }
	//remove image tag
	$entry = preg_replace('/<img [^/>]*src=(\"|\').+?(\1)[^>]*\/*>/','', $entry); /* */
	//remove any empty tags left by the scrape.
	$entry = str_replace('<p> </p>', '', $entry);
	$entry = preg_replace( '|< ([a-z]+)[^>]*>\s*|i', '', $entry );
	$entry = preg_replace( '|< ([a-z]+)[^>]*>\s*|i', '', $entry );
	$entry = preg_replace( '|< ([a-z]+)[^>]*>\s*|i', '', $entry );
	return $entry;
}