Mars has definitely gone to the dark side. The introduced Dark Chocolate M&Ms in Regular and Peanut first as a tie in to Star Wars in late 2005 (see the MPire website). Called the Darth Mix (CandyBlog review), they sported a different mix of colors. Then last year Mars made Regular Dark Chocolate M&Ms part of their regular line. Nothing was heard from the Dark Chocolate Peanut M&Ms.
Continuing the dark trend, Mars also gave the Snickers bar a limited edition dark coating, which has now been adopted into the regular line as it's been spotted in stores without "limited edition" on the wrappers.
But now it appears that Mars will be bringing the M&Ms Dark Chocolate Peanuts back as a regular product starting July 1, 2007 with the tagline, "Finally....you'll be NUTS about the dark!"
Official Website. (Source All Candy Expo)
UPDATE: M&Ms Dark Chocolate Peanut are now available in stores. I spotted them at Rite Aid in Los Angeles last night.